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| 1 : | apizer | 1080 | |
| 2 : | sh002i | 1050 | #use strict; |
| 3 : | |||
| 4 : | ########### | ||
| 5 : | #use Carp; | ||
| 6 : | |||
| 7 : | =head1 NAME | ||
| 8 : | |||
| 9 : | Numerical methods for the PG language | ||
| 10 : | |||
| 11 : | =head1 SYNPOSIS | ||
| 12 : | |||
| 13 : | |||
| 14 : | |||
| 15 : | =head1 DESCRIPTION | ||
| 16 : | |||
| 17 : | =cut | ||
| 18 : | |||
| 19 : | =head2 Interpolation methods | ||
| 20 : | |||
| 21 : | =head3 Plotting a list of points (piecewise linear interpolation) | ||
| 22 : | |||
| 23 : | |||
| 24 : | Usage: plot_list([x0,y0,x1,y1,...]); | ||
| 25 : | plot_list([(x0,y0),(x1,y1),...]); | ||
| 26 : | plot_list(\x_y_array); | ||
| 27 : | apizer | 1080 | |
| 28 : | sh002i | 1050 | plot_list([x0,x1,x2...], [y0,y1,y2,...]); |
| 29 : | plot_list(\@xarray,\@yarray); | ||
| 30 : | |||
| 31 : | |||
| 32 : | =cut | ||
| 33 : | |||
| 34 : | BEGIN { | ||
| 35 : | be_strict(); | ||
| 36 : | } | ||
| 37 : | sub _PGnumericalmacros_init { | ||
| 38 : | } | ||
| 39 : | |||
| 40 : | sub plot_list { | ||
| 41 : | my($xref,$yref) = @_; | ||
| 42 : | unless( defined($xref) && ref($xref) =~/ARRAY/ ) { | ||
| 43 : | die "Error in plot_list:X values must be given as an array reference. | ||
| 44 : | Remember to use ~~\@array to reference an array in the PG language."; | ||
| 45 : | } | ||
| 46 : | if (defined($yref) && ! ( ref($yref) =~/ARRAY/ ) ) { | ||
| 47 : | die "Error in plot_list:Y values must be given as an array reference. | ||
| 48 : | Remember to use ~~\@array to reference an array in the PG language."; | ||
| 49 : | } | ||
| 50 : | my (@x_vals, @y_vals); | ||
| 51 : | unless( defined($yref) ) { #with only one entry we assume (x0,y0,x1,y1..); | ||
| 52 : | if ( @$xref % 2 ==1) { | ||
| 53 : | apizer | 1080 | die "ERROR in plot_list -- single array of input has odd number of |
| 54 : | sh002i | 1050 | elements"; |
| 55 : | } | ||
| 56 : | apizer | 1080 | |
| 57 : | sh002i | 1050 | my @in = @$xref; |
| 58 : | while (@in) { | ||
| 59 : | push(@x_vals, shift(@in)); | ||
| 60 : | push(@y_vals, shift(@in)); | ||
| 61 : | } | ||
| 62 : | $xref = \@x_vals; | ||
| 63 : | $yref = \@y_vals; | ||
| 64 : | apizer | 1080 | } |
| 65 : | |||
| 66 : | sh002i | 1050 | my $fun =sub { |
| 67 : | my $x = shift; | ||
| 68 : | my $y; | ||
| 69 : | my( $x0,$x1,$y0,$y1); | ||
| 70 : | my @x_values = @$xref; | ||
| 71 : | my @y_values = @$yref; | ||
| 72 : | while (( @x_values and $x > $x_values[0]) or | ||
| 73 : | ( @x_values > 0 and $x >= $x_values[0] ) ) { | ||
| 74 : | $x0 = shift(@x_values); | ||
| 75 : | $y0 = shift(@y_values); | ||
| 76 : | } | ||
| 77 : | # now that we have the left hand of the input | ||
| 78 : | #check first that x isn't out of range to the left or right | ||
| 79 : | if (@x_values && defined($x0) ) { | ||
| 80 : | $x1= shift(@x_values); | ||
| 81 : | $y1=shift(@y_values); | ||
| 82 : | $y = $y0 + ($y1-$y0)*($x-$x0)/($x1-$x0); | ||
| 83 : | } | ||
| 84 : | $y; | ||
| 85 : | }; | ||
| 86 : | $fun; | ||
| 87 : | } | ||
| 88 : | |||
| 89 : | =head3 Horner polynomial/ Newton polynomial | ||
| 90 : | |||
| 91 : | |||
| 92 : | |||
| 93 : | Usege: $fn = horner([x0,x1,x2],[q0,q1,q2]); | ||
| 94 : | Produces the newton polynomial | ||
| 95 : | &$fn(x) = q0 + q1*(x-x0) +q2*(x-x1)*(x-x0); | ||
| 96 : | |||
| 97 : | Generates a subroutine which evaluates a polynomial passing through the points C<(x0,q0), (x1,q1), | ||
| 98 : | apizer | 1080 | ... > using Horner's method. |
| 99 : | sh002i | 1050 | |
| 100 : | =cut | ||
| 101 : | |||
| 102 : | sub horner { | ||
| 103 : | my ($xref,$qref) = @_; # get the coefficients | ||
| 104 : | my $fn = sub { | ||
| 105 : | my $x = shift; | ||
| 106 : | my @xvals = @$xref; | ||
| 107 : | my @qvals = @$qref; | ||
| 108 : | my $y = pop(@qvals); | ||
| 109 : | pop(@xvals); | ||
| 110 : | while (@qvals) { | ||
| 111 : | $y = $y * ($x - pop(@xvals) ) + pop(@qvals); | ||
| 112 : | } | ||
| 113 : | $y; | ||
| 114 : | }; | ||
| 115 : | $fn; | ||
| 116 : | } | ||
| 117 : | |||
| 118 : | |||
| 119 : | =head3 Hermite polynomials | ||
| 120 : | |||
| 121 : | |||
| 122 : | =pod | ||
| 123 : | |||
| 124 : | Usage: $poly = hermit([x0,x1...],[y0,y1...],[yp0,yp1,...]); | ||
| 125 : | apizer | 1080 | Produces a reference to polynomial function |
| 126 : | sh002i | 1050 | with the specified values and first derivatives |
| 127 : | at (x0,x1,...). | ||
| 128 : | &$poly(34) gives a number | ||
| 129 : | |||
| 130 : | Generates a subroutine which evaluates a polynomial passing through the specified points | ||
| 131 : | with the specified derivatives: (x0,y0,yp0) ... | ||
| 132 : | The polynomial will be of high degree and may wobble unexpectedly. Use the Hermite splines | ||
| 133 : | described below and in Hermite.pm for most graphing purposes. | ||
| 134 : | |||
| 135 : | =cut | ||
| 136 : | |||
| 137 : | |||
| 138 : | sub hermite { | ||
| 139 : | my($x_ref,$y_ref,$yp_ref) = @_; | ||
| 140 : | my (@zvals,@qvals); | ||
| 141 : | my $n = $#{$x_ref}; | ||
| 142 : | my $i =0; | ||
| 143 : | foreach $i (0..$n ) { | ||
| 144 : | $zvals[2*$i] = $$x_ref[$i]; | ||
| 145 : | $zvals[2*$i+1] = $$x_ref[$i]; | ||
| 146 : | $qvals[2*$i][0] = $$y_ref[$i]; | ||
| 147 : | $qvals[2*$i+1][0] = $$y_ref[$i]; | ||
| 148 : | $qvals[2*$i+1][1] = $$yp_ref[$i]; | ||
| 149 : | apizer | 1080 | $qvals[2*$i][1] = ( $qvals[2*$i][0] - $qvals[2*$i-1][0] ) |
| 150 : | sh002i | 1050 | / ( $zvals[2*$i]- $zvals[2*$i-1] ) unless $i ==0; |
| 151 : | apizer | 1080 | |
| 152 : | sh002i | 1050 | } |
| 153 : | my $j; | ||
| 154 : | foreach $i ( 2..(2*$n+1) ) { | ||
| 155 : | foreach $j (2 .. $i) { | ||
| 156 : | $qvals[$i][$j] = ($qvals[$i][$j-1] - $qvals[$i-1][$j-1]) / | ||
| 157 : | ($zvals[$i] - $zvals[$i-$j]); | ||
| 158 : | } | ||
| 159 : | } | ||
| 160 : | my @output; | ||
| 161 : | foreach $i (0..2*$n+1) { | ||
| 162 : | push(@output,$qvals[$i][$i]); | ||
| 163 : | } | ||
| 164 : | apizer | 1080 | horner(\@zvals,\@output); |
| 165 : | sh002i | 1050 | } |
| 166 : | |||
| 167 : | |||
| 168 : | =head3 Hermite splines | ||
| 169 : | |||
| 170 : | |||
| 171 : | Usage: $spline = hermit_spline([x0,x1...],[y0,y1...],[yp0,yp1,...]); | ||
| 172 : | Produces a reference to a piecewise cubic hermit spline | ||
| 173 : | with the specified values and first derivatives | ||
| 174 : | at (x0,x1,...). | ||
| 175 : | apizer | 1080 | |
| 176 : | sh002i | 1050 | &$spline(45) evaluates to a number. |
| 177 : | |||
| 178 : | Generates a subroutine which evaluates a piecewise cubic polynomial | ||
| 179 : | passing through the specified points | ||
| 180 : | with the specified derivatives: (x0,y0,yp0) ... | ||
| 181 : | |||
| 182 : | An object oriented version of this is defined in Hermite.pm | ||
| 183 : | |||
| 184 : | =cut | ||
| 185 : | |||
| 186 : | |||
| 187 : | sub hermite_spline { | ||
| 188 : | my ($xref, $yref, $ypref) = @_; | ||
| 189 : | my @xvals = @$xref; | ||
| 190 : | my @yvals = @$yref; | ||
| 191 : | my @ypvals = @$ypref; | ||
| 192 : | my $x0 = shift @xvals; | ||
| 193 : | my $y0 = shift @yvals; | ||
| 194 : | my $yp0 = shift @ypvals; | ||
| 195 : | my ($x1,$y1,$yp1); | ||
| 196 : | my @polys; #calculate a hermite polynomial evaluator for each region | ||
| 197 : | while (@xvals) { | ||
| 198 : | $x1 = shift @xvals; | ||
| 199 : | $y1 = shift @yvals; | ||
| 200 : | $yp1 = shift @ypvals; | ||
| 201 : | push @polys, hermite([$x0,$x1],[$y0,$y1],[$yp0,$yp1]); | ||
| 202 : | $x0 = $x1; | ||
| 203 : | $y0 = $y1; | ||
| 204 : | $yp0 = $yp1; | ||
| 205 : | } | ||
| 206 : | apizer | 1080 | |
| 207 : | |||
| 208 : | sh002i | 1050 | my $hermite_spline_sub = sub { |
| 209 : | my $x = shift; | ||
| 210 : | my $y; | ||
| 211 : | my $fun; | ||
| 212 : | my @xvals = @$xref; | ||
| 213 : | my @fns = @polys; | ||
| 214 : | return $y=&{$fns[0]} ($x) if $x == $xvals[0]; #handle left most endpoint | ||
| 215 : | apizer | 1080 | |
| 216 : | sh002i | 1050 | while (@xvals && $x > $xvals[0]) { # find the function for this range of x |
| 217 : | shift(@xvals); | ||
| 218 : | $fun = shift(@fns); | ||
| 219 : | } | ||
| 220 : | apizer | 1080 | |
| 221 : | sh002i | 1050 | # now that we have the left hand of the input |
| 222 : | #check first that x isn't out of range to the left or right | ||
| 223 : | if (@xvals && defined($fun) ) { | ||
| 224 : | $y =&$fun($x); | ||
| 225 : | } | ||
| 226 : | $y; | ||
| 227 : | }; | ||
| 228 : | $hermite_spline_sub; | ||
| 229 : | } | ||
| 230 : | |||
| 231 : | =head3 Cubic spline approximation | ||
| 232 : | |||
| 233 : | |||
| 234 : | |||
| 235 : | Usage: | ||
| 236 : | $fun_ref = cubic_spline(~~@x_values, ~~@y_values); | ||
| 237 : | apizer | 1080 | |
| 238 : | sh002i | 1050 | Where the x and y value arrays come from the function to be approximated. |
| 239 : | The function reference will take a single value x and produce value y. | ||
| 240 : | |||
| 241 : | $y = &$fun_ref($x); | ||
| 242 : | apizer | 1080 | |
| 243 : | sh002i | 1050 | You can also generate javaScript which defines a cubic spline: |
| 244 : | |||
| 245 : | $function_string = javaScript_cubic_spline(~~@_x_values, ~~@y_values, | ||
| 246 : | name => 'myfunction1', | ||
| 247 : | llimit => -3, | ||
| 248 : | rlimit => 3, | ||
| 249 : | ); | ||
| 250 : | |||
| 251 : | The string contains | ||
| 252 : | |||
| 253 : | <SCRIPT LANGUAGE="JavaScript"> | ||
| 254 : | <!-- Begin | ||
| 255 : | function myfunction1(x) { | ||
| 256 : | ...etc... | ||
| 257 : | } | ||
| 258 : | </SCRIPT> | ||
| 259 : | |||
| 260 : | apizer | 1080 | and can be placed in the header of the HTML output using |
| 261 : | sh002i | 1050 | |
| 262 : | HEADER_TEXT($function_string); | ||
| 263 : | |||
| 264 : | =cut | ||
| 265 : | |||
| 266 : | sub cubic_spline { | ||
| 267 : | my($t_ref, $y_ref) = @_; | ||
| 268 : | my @spline_coeff = create_cubic_spline($t_ref, $y_ref); | ||
| 269 : | sub { | ||
| 270 : | my $x = shift; | ||
| 271 : | eval_cubic_spline($x,@spline_coeff); | ||
| 272 : | } | ||
| 273 : | } | ||
| 274 : | sub eval_cubic_spline { | ||
| 275 : | apizer | 1080 | my ($x, $t_ref,$a_ref,$b_ref,$c_ref,$d_ref ) = @_; |
| 276 : | sh002i | 1050 | # The knot points given by $t_ref should be in order. |
| 277 : | my $i=0; | ||
| 278 : | my $out =0; | ||
| 279 : | while (defined($t_ref->[$i+1] ) && $x > $t_ref->[$i+1] ) { | ||
| 280 : | apizer | 1080 | |
| 281 : | sh002i | 1050 | $i++; |
| 282 : | } | ||
| 283 : | unless (defined($t_ref->[$i]) && ( $t_ref->[$i] <= $x ) && ($x <= $t_ref->[$i+1] ) ) { | ||
| 284 : | $out = undef; | ||
| 285 : | # input value is not in the range defined by the function. | ||
| 286 : | } else { | ||
| 287 : | apizer | 1080 | $out = ( $t_ref->[$i+1] - $x )* ( ($d_ref->[$i]) +($a_ref->[$i])*( $t_ref->[$i+1] - $x )**2 ) |
| 288 : | sh002i | 1050 | + |
| 289 : | apizer | 1080 | ( $x - $t_ref->[$i] ) * ( ($b_ref->[$i])*( $x - $t_ref->[$i] )**2 + ($c_ref->[$i]) ) |
| 290 : | |||
| 291 : | } | ||
| 292 : | sh002i | 1050 | $out; |
| 293 : | } | ||
| 294 : | |||
| 295 : | ########################################################################## | ||
| 296 : | # Cubic spline algorithm adapted from p319 of Kincaid and Cheney's Numerical Analysis | ||
| 297 : | ########################################################################## | ||
| 298 : | |||
| 299 : | sub create_cubic_spline { | ||
| 300 : | my($t_ref, $y_ref) = @_; | ||
| 301 : | # The knot points are given by $t_ref (in order) and the function values by $y_ref | ||
| 302 : | my $num =$#{$t_ref}; # number of knots | ||
| 303 : | my $i; | ||
| 304 : | my (@h,@b,@u,@v,@z); | ||
| 305 : | foreach $i (0..$num-1) { | ||
| 306 : | $h[$i] = $t_ref->[$i+1] - $t_ref->[$i]; | ||
| 307 : | $b[$i] = 6*( $y_ref->[$i+1] - $y_ref->[$i] )/$h[$i]; | ||
| 308 : | } | ||
| 309 : | $u[1] = 2*($h[0] +$h[1] ); | ||
| 310 : | $v[1] = $b[1] - $b[0]; | ||
| 311 : | foreach $i (2..$num-1) { | ||
| 312 : | $u[$i] = 2*( $h[$i] + $h[$i-1] ) - ($h[$i-1])**2/$u[$i-1]; | ||
| 313 : | $v[$i] = $b[$i] - $b[$i-1] - $h[$i-1]*$v[$i-1]/$u[$i-1] | ||
| 314 : | } | ||
| 315 : | $z[$num] = 0; | ||
| 316 : | for ($i = $num-1; $i>0; $i--) { | ||
| 317 : | $z[$i] = ( $v[$i] - $h[$i]*$z[$i+1] )/$u[$i]; | ||
| 318 : | } | ||
| 319 : | $z[0] = 0; | ||
| 320 : | my ($a_ref, $b_ref, $c_ref, $d_ref); | ||
| 321 : | foreach $i (0..$num-1) { | ||
| 322 : | $a_ref->[$i] = $z[$i]/(6*$h[$i]); | ||
| 323 : | $b_ref->[$i] = $z[$i+1]/(6*$h[$i]); | ||
| 324 : | $c_ref->[$i] = ( ($y_ref->[$i+1])/$h[$i] - $z[$i+1]*$h[$i]/6 ); | ||
| 325 : | $d_ref->[$i] = ( ($y_ref->[$i])/$h[$i] - $z[$i]*$h[$i]/6 ); | ||
| 326 : | } | ||
| 327 : | ($t_ref, $a_ref, $b_ref, $c_ref, $d_ref); | ||
| 328 : | } | ||
| 329 : | |||
| 330 : | |||
| 331 : | sub javaScript_cubic_spline { | ||
| 332 : | my $x_ref = shift; | ||
| 333 : | my $y_ref = shift; | ||
| 334 : | my %options = @_; | ||
| 335 : | apizer | 1080 | assign_option_aliases(\%options, |
| 336 : | |||
| 337 : | sh002i | 1050 | ); |
| 338 : | set_default_options(\%options, | ||
| 339 : | name => 'func', | ||
| 340 : | llimit => $x_ref->[0], | ||
| 341 : | rlimit => $x_ref->[$#$x_ref], | ||
| 342 : | ); | ||
| 343 : | apizer | 1080 | |
| 344 : | sh002i | 1050 | my ($t_ref, $a_ref, $b_ref, $c_ref, $d_ref) = create_cubic_spline ($x_ref, $y_ref); |
| 345 : | |||
| 346 : | |||
| 347 : | my $str_t_array = "t = new Array(" . join(",",@$t_ref) . ");"; | ||
| 348 : | my $str_a_array = "a = new Array(" . join(",",@$a_ref) . ");"; | ||
| 349 : | my $str_b_array = "b = new Array(" . join(",",@$b_ref) . ");"; | ||
| 350 : | my $str_c_array = "c = new Array(" . join(",",@$c_ref) . ");"; | ||
| 351 : | my $str_d_array = "d = new Array(" . join(",",@$d_ref) . ");"; | ||
| 352 : | |||
| 353 : | my $output_str = <<END_OF_JAVA_TEXT; | ||
| 354 : | <SCRIPT LANGUAGE="JavaScript"> | ||
| 355 : | <!-- Begin | ||
| 356 : | |||
| 357 : | |||
| 358 : | |||
| 359 : | function $options{name}(x) { | ||
| 360 : | $str_t_array | ||
| 361 : | $str_a_array | ||
| 362 : | $str_b_array | ||
| 363 : | $str_c_array | ||
| 364 : | $str_d_array | ||
| 365 : | apizer | 1080 | |
| 366 : | sh002i | 1050 | // Evaluate a cubic spline defined by the vectors above |
| 367 : | i = 0; | ||
| 368 : | while (x > t[i+1] ) { | ||
| 369 : | i++ | ||
| 370 : | } | ||
| 371 : | apizer | 1080 | |
| 372 : | sh002i | 1050 | if ( t[i] <= x && x <= t[i+1] && $options{llimit} <= x && x <= $options{rlimit} ) { |
| 373 : | return ( ( t[i+1] - x )*( d[i] +a[i]*( t[i+1] - x )*( t[i+1] - x ) ) | ||
| 374 : | apizer | 1080 | + ( x - t[i] )*( b[i]*( x - t[i])*( x - t[i] ) +c[i] ) |
| 375 : | sh002i | 1050 | ); |
| 376 : | |||
| 377 : | } else { | ||
| 378 : | return( "undefined" ) ; | ||
| 379 : | } | ||
| 380 : | |||
| 381 : | } | ||
| 382 : | apizer | 1080 | // End |
| 383 : | sh002i | 1050 | --> |
| 384 : | </SCRIPT> | ||
| 385 : | <NOSCRIPT> | ||
| 386 : | This problem requires a browser capable of processing javaScript | ||
| 387 : | </NOSCRIPT> | ||
| 388 : | END_OF_JAVA_TEXT | ||
| 389 : | |||
| 390 : | $output_str; | ||
| 391 : | } | ||
| 392 : | |||
| 393 : | |||
| 394 : | =head2 Numerical Integration methods | ||
| 395 : | |||
| 396 : | =head3 Integration by trapezoid rule | ||
| 397 : | |||
| 398 : | =pod | ||
| 399 : | |||
| 400 : | Usage: trapezoid(function_reference, start, end, steps=>30 ); | ||
| 401 : | |||
| 402 : | Implements the trapezoid rule using 30 intervals between 'start' and 'end'. | ||
| 403 : | The first three arguments are required. The final argument (number of steps) | ||
| 404 : | is optional and defaults to 30. | ||
| 405 : | |||
| 406 : | =cut | ||
| 407 : | |||
| 408 : | |||
| 409 : | sub trapezoid { | ||
| 410 : | my $fn_ref = shift; | ||
| 411 : | my $x0 = shift; | ||
| 412 : | my $x1 = shift; | ||
| 413 : | my %options = @_; | ||
| 414 : | apizer | 1080 | assign_option_aliases(\%options, |
| 415 : | sh002i | 1050 | intervals => 'steps', |
| 416 : | ); | ||
| 417 : | set_default_options(\%options, | ||
| 418 : | steps => 30, | ||
| 419 : | ); | ||
| 420 : | my $steps = $options{steps}; | ||
| 421 : | my $delta =($x1-$x0)/$steps; | ||
| 422 : | my $i; | ||
| 423 : | my $sum=0; | ||
| 424 : | foreach $i (1..($steps-1) ) { | ||
| 425 : | $sum =$sum + &$fn_ref( $x0 + $i*$delta ); | ||
| 426 : | } | ||
| 427 : | $sum = $sum + 0.5*( &$fn_ref($x0) + &$fn_ref($x1) ); | ||
| 428 : | $sum*$delta; | ||
| 429 : | } | ||
| 430 : | |||
| 431 : | =head3 Romberg method of integration | ||
| 432 : | |||
| 433 : | =pod | ||
| 434 : | |||
| 435 : | Usage: romberg(function_reference, x0, x1, level); | ||
| 436 : | |||
| 437 : | Implements the Romberg integration routine through 'level' recursive steps. Level defaults to 6. | ||
| 438 : | |||
| 439 : | =cut | ||
| 440 : | |||
| 441 : | |||
| 442 : | sub romberg { | ||
| 443 : | my $fn_ref = shift; | ||
| 444 : | my $x0 = shift; | ||
| 445 : | my $x1 = shift; | ||
| 446 : | my %options = @_; | ||
| 447 : | set_default_options(\%options, | ||
| 448 : | level => 6, | ||
| 449 : | ); | ||
| 450 : | my $level = $options{level}; | ||
| 451 : | romberg_iter($fn_ref, $x0,$x1, $level,$level); | ||
| 452 : | } | ||
| 453 : | |||
| 454 : | sub romberg_iter { | ||
| 455 : | my $fn_ref = shift; | ||
| 456 : | my $x0 = shift; | ||
| 457 : | my $x1 = shift; | ||
| 458 : | my $j = shift; | ||
| 459 : | my $k = shift; | ||
| 460 : | my $out; | ||
| 461 : | if ($k == 1 ) { | ||
| 462 : | $out = trapezoid($fn_ref, $x0,$x1,steps => 2**($j-1) ); | ||
| 463 : | } else { | ||
| 464 : | apizer | 1080 | |
| 465 : | sh002i | 1050 | $out = ( 4**($k-1) * romberg_iter($fn_ref, $x0,$x1,$j,$k-1) - |
| 466 : | romberg_iter($fn_ref, $x0,$x1,$j-1,$k-1) ) / ( 4**($k-1) -1) ; | ||
| 467 : | } | ||
| 468 : | $out; | ||
| 469 : | } | ||
| 470 : | |||
| 471 : | =head3 Inverse Romberg | ||
| 472 : | |||
| 473 : | =pod | ||
| 474 : | |||
| 475 : | Usage: inv_romberg(function_reference, a, value); | ||
| 476 : | |||
| 477 : | Finds b such that the integral of the function from a to b is equal to value. | ||
| 478 : | Assumes that the function is continuous and doesn't take on the zero value. | ||
| 479 : | apizer | 1080 | Uses Newton's method of approximating roots of equations, and Romberg to evaluate definite integrals. |
| 480 : | sh002i | 1050 | |
| 481 : | =cut | ||
| 482 : | |||
| 483 : | sub inv_romberg { | ||
| 484 : | my $fn_ref = shift; | ||
| 485 : | my $a = shift; | ||
| 486 : | my $value = shift; | ||
| 487 : | my $b = $a; | ||
| 488 : | my $delta = 1; | ||
| 489 : | apizer | 1080 | my $i=0; |
| 490 : | sh002i | 1050 | my $funct; |
| 491 : | my $deriv; | ||
| 492 : | apizer | 1080 | while (abs($delta) > 0.000001 && $i < 5000) { |
| 493 : | sh002i | 1050 | $funct = romberg($fn_ref,$a,$b)-$value; |
| 494 : | $deriv = &$fn_ref ( $b ); | ||
| 495 : | if ($deriv == 0) { | ||
| 496 : | warn 'Values of the function are too close to 0.'; | ||
| 497 : | return; | ||
| 498 : | apizer | 1080 | } |
| 499 : | sh002i | 1050 | $delta = $funct/$deriv; |
| 500 : | apizer | 1080 | $b = $b - $delta; |
| 501 : | sh002i | 1050 | $i++; |
| 502 : | apizer | 1080 | } |
| 503 : | sh002i | 1050 | if ($i == 5000) { |
| 504 : | warn 'Newtons method does not converge.'; | ||
| 505 : | apizer | 1080 | return; |
| 506 : | sh002i | 1050 | } |
| 507 : | $b; | ||
| 508 : | apizer | 1080 | } |
| 509 : | sh002i | 1050 | |
| 510 : | ######################################################### | ||
| 511 : | gage | 4318 | =pod |
| 512 : | sh002i | 1050 | |
| 513 : | gage | 4318 | rungeKutta4 |
| 514 : | |||
| 515 : | Finds integral curve of a vector field using the 4th order Runge Kutta method. | ||
| 516 : | |||
| 517 : | Useage: rungeKutta4( &vectorField(t,x),%options); | ||
| 518 : | |||
| 519 : | Returns: \@array of points [t,y}) | ||
| 520 : | |||
| 521 : | Default %options: | ||
| 522 : | 'initial_t' => 1, | ||
| 523 : | 'initial_y' => 1, | ||
| 524 : | 'dt' => .01, | ||
| 525 : | 'num_of_points' => 10, #number of reported points | ||
| 526 : | 'interior_points' => 5, # number of 'interior' steps between reported points | ||
| 527 : | 'debug' | ||
| 528 : | |||
| 529 : | =cut | ||
| 530 : | |||
| 531 : | sub rungeKutta4 { | ||
| 532 : | gage | 4767 | my $rf_fun = shift; |
| 533 : | gage | 4318 | my %options = @_; |
| 534 : | set_default_options( \%options, | ||
| 535 : | 'initial_t' => 1, | ||
| 536 : | 'initial_y' => 1, | ||
| 537 : | 'dt' => .01, | ||
| 538 : | 'num_of_points' => 10, #number of reported points | ||
| 539 : | 'interior_points' => 5, # number of 'interior' steps between reported points | ||
| 540 : | 'debug' => 1, # remind programmers to always pass the debug parameter | ||
| 541 : | ); | ||
| 542 : | my $t = $options{initial_t}; | ||
| 543 : | my $y = $options{initial_y}; | ||
| 544 : | |||
| 545 : | my $num = $options{'num_of_points'}; # number of points | ||
| 546 : | my $num2 = $options{'interior_points'}; # number of steps between points. | ||
| 547 : | my $dt = $options{'dt'}; | ||
| 548 : | my $errors = undef; | ||
| 549 : | my $rf_rhs = sub { my @in = @_; | ||
| 550 : | my ( $out, $err) = &$rf_fun(@in); | ||
| 551 : | $errors .= " $err at ( ".join(" , ", @in) . " )<br>\n" if defined($err); | ||
| 552 : | $out = 'NaN' if defined($err) and not is_a_number($out); | ||
| 553 : | $out; | ||
| 554 : | }; | ||
| 555 : | |||
| 556 : | my @output = ([$t, $y]); | ||
| 557 : | my ($i, $j, $K1,$K2,$K3,$K4); | ||
| 558 : | |||
| 559 : | for ($j=0; $j<$num; $j++) { | ||
| 560 : | for ($i=0; $i<$num2; $i++) { | ||
| 561 : | $K1 = $dt*&$rf_rhs($t, $y); | ||
| 562 : | $K2 = $dt*&$rf_rhs($t+$dt/2,$y+$K1/2); | ||
| 563 : | $K3 = $dt*&$rf_rhs($t+$dt/2, $y+$K2/2); | ||
| 564 : | $K4 = $dt*&$rf_rhs($t+$dt, $y+$K3); | ||
| 565 : | $y = $y + ($K1 + 2*$K2 + 2*$K3 + $K4)/6; | ||
| 566 : | $t = $t + $dt; | ||
| 567 : | } | ||
| 568 : | push(@output, [$t, $y]); | ||
| 569 : | } | ||
| 570 : | if (defined $errors) { | ||
| 571 : | return $errors; | ||
| 572 : | } else { | ||
| 573 : | return \@output; | ||
| 574 : | } | ||
| 575 : | } | ||
| 576 : | |||
| 577 : | |||
| 578 : | |||
| 579 : | sh002i | 1050 | 1; |
| 580 : |
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