Reduced row echelon form: Difference between revisions

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''Reduced Row Echelon Form''   (a.k.a.   ''row canonical form'')   of a matrix, with optimization added.
<lang rexx>/*REXX pgm performs Reduced Row Echelon Form (RREF), AKA row canonical form on a matrix)*/
cols= 0; w= 0; @. =0 /*max cols in a row; max width; matrix.*/
mat.=; mat.1= ' 1 2 -1 -4 '
mat.2= ' 2 3 -1 -11 '
mat.3= ' -2 0 -3 22 '
do r=1 until mat.r==''; _=mat.r /*build @.row.col from (matrix) mat.X*/
do c=1 until _=''; parse var _ @.r.c _
w= max(w, length(@.r.c) + 1) /*find the maximum width of an element.*/
end /*c*/
cols= max(cols, c) /*save the maximum number of columns. */
end /*r*/
rows= r - 1 /*adjust the row count (from DO loop). */
call showMat 'original matrix' /*display the original matrix to screenmatrix──►screen.*/
!=1 1 /*set the working column pointer to 1.*/
/* ┌──────────────────────◄────────────────◄──── Reduced Row Echelon Form on matrix.*/
do r=1 for rows while cols>! /*begin to perform the heavy lifting. */
j=r r /*use a subsitute index for the DO loop*/
do while @.j.!==0; j= j + 1
if j==rows then do; j= r; != ! + 1; if cols==! then leave r; end
end /*while*/
/* [↓] swap rows J,R (but not if same)*/
do _=1 for cols while j\==r; parse value @.r._ @.j._ with @.j._ @._._
end /*_*/
?= @.r.!
do d=1 for cols while ?\=1; @.r.d= @.r.d / ?
end /*d*/ /* [↑] divide row J by @.r.p ──unless≡1*/
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end /*s*/
end /*k*/ /* [↑] for the rest of numbers in row.*/
!= ! + 1 /*bump the working column pointer. */
end /*r*/
 
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exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
showMat: parse arg title; say; say center(title, 3 + (cols+1) * w, '─'); say
do r=1 for rows; _=
do c=1 for cols
if @.r.c=='' then do; say "***error*** matrix element isn't defined:"
say 'row' r", column" c'.'; exit 13
end
_= _ right(@.r.c, w)
end /*c*/
say _ say _ /*display a matrix row to the terminal.*/
end /*r*/; return</lang>
{{out|output|text=&nbsp; when using the default (internal) input:}}
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