8.1 C output of piecewise functions (6.3.01)

8.1.1 Maneesh Yadav

In trying to produce C output of a piecewise function (actually it’s piecewise derivative), the output has the word piecewise instead of splitting things up into ’if’ and ’then’...is there something I am missing?

How can get C output that I can directly use? Is there a macro or lib I need to link to?

Manual editing isn’t really an option since we actually have to generate a large file with lots of equations of this nature.

8.1.2 Robert Israel (7.3.01)

This is what "prep2trans" in the codegen package is for. For example:

> f:= proc(x,y) piecewise(x<3*y,x,y) end; 
  with(codegen): 
  g:= prep2trans(f): 
  C(g); 
 
double g(x,y) 
double x; 
double y; 
{ 
  { 
    if( x < 3.0*y ) 
      return(x); 
    else 
      return(y); 
  } 
}
 

It also handles procedures involving "sum" or "add". However, I just noticed a bug: it doesn’t seem to like a "piecewise" inside a "sum" or "add": e.g.

> f:= proc(x,y) local i; add(piecewise(x<i*y,x,y),i=1..3) end; 
  g:= prep2trans(f); 
 
Error, (in intrep/StatSeq) invalid terms in sum