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Newsgroups: comp.graphics.apps.gnuplot
Date: Wed, 28 Aug 2019 12:01:04 -0700 (PDT)
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Subject: User function in "using" expression
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Xref: csiph.com comp.graphics.apps.gnuplot:4215

I'm trying to use gnuplot to solve a specific version of the problem
 
3d plot z(x,y) with x,ys subject to the constraint f(x,y)=0
 
The following works (the files are 0 contours captured by set table)

array n[6]
file(i) = sprintf("coma%d.gpt",i)
splot for [i=1:|n|] file(i) using 1:2:(0):(0):(0):(1) with vectors

but if I also do:

phi(x,y) = (1+x)/(1+sqrt(1+(x*x-1)*y))
spher(n,x,y) = (f=phi(x,y),n2=n*n,((f-n)^2*(f-n2)*(1-y*f)-f^3)/(n2*(n-1)^3))
splot for [i=1:|n|] file(i) using 1:2:(0):(0):(0):(spher(n[i],$1,$2)) with vectors

I get the following message:

 non-integer passed to boolean operator

What am I missing? I can provide the full file if needed.

Al