Euler method: Difference between revisions

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<br>It also shows the percentage difference (analytic vs. Euler's method) for each calculation.

<lang rexx>/*REXX pgm solves example of Newton's cooling law via Euler's method (diff. step sizes).*/

e=2.718281828459045235360287471352662497757247093699959574966967627724076630353547595

numeric digits length( e() ) - length(.) /*use the number of decimal digits in E*/

numeric digits length(e) - length(.) /*use the number of decimal digits in E*/

parse arg Ti Tr cc tt ss /*obtain optional arguments from the CL*/

if Ti='' | Ti="," then Ti= 100 /*given? Default: initial temp in ºC.*/

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exit /*stick a fork in it, we're all done. */

/*──────────────────────────────────────────────────────────────────────────────────────*/

exp: procedure expose e; arg x; ix= x%1; if abs(x-ix)>.5 then ix=ix+sign(x); x= x-ix; z=1

e: return 2.718281828459045235360287471352662497757247093699959574966967627724076630353548

_=1; w=1; do j=1; _= _*x/j; z= (z+_)/1; if z==w then leave; w=z

/*──────────────────────────────────────────────────────────────────────────────────────*/

end /*j*/; if z\==0 then z= e**ix * z; return z</lang>

exp: procedure; ~~parse~~ arg x; ix= x%1; if abs(x-ix)>.5 then ix= ix+sign(x); x=x-ix; z=1

_=1; w=1; do j=1; _= _*x/j; z= (z+_)/1; if z==w then leave; w=z

end /*j*/; if z\==0 then z= e()**ix * z; return z</lang>

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