Mike Williams wrote:

> Wasn't it Justace Clutter who wrote:
>>I am trying to get render a frame with a wave function built in it.  The
>>function is the specific solution after seperation of variables was done.
>>Anyway all that is irrelelvant.  When I try to render the frame it just
>>sits there and does nothing.  the povray process accums time but does not
>>do anyhing and I have to kill it with a sig 9 to get it to exit.  I use
>>Linux if you have not already guessed.  Any information on this would be
>>wonderfull.
>>
> 
> A fairly minimal piece of code that exhibits the problem is
> 
> // This is the entire scene file
> #declare F = function {sum(n, 1, 1, 1*(2/(n*1)))}
> #debug str(F(0,0,0),5,5)
> // -----------------------------
> 
> Any attempt to simplify the expression causes the scene to complete, but
> does not always return what I consider the right answer.
> 
> 
> Consider these:-
> 
>   #declare F = function {sum(n, 1, 1, n)}
> 
> evaluates to 1.00000, which I reckon is OK, but
> 
>   #declare F = function {sum(n, 1, 1, 1*n)}
> 
> evaluates to 2.00000, which I reckon is wrong.
> 
> 
>   #declare F = function {sum(n, 3.1234, 4.1234, 1)}   => 2.00000 : OK
>   #declare F = function {sum(n, 3.1234, 4.1234, 1*1)} => 5.12340
>            which is wrong by an amount equal to the initial value of n.
> 
>   #declare F = function {prod(n, 1,2, n)}     =>  2.00000 : OK
>   #declare F = function {prod(n, 1,2, 1*n)}   =>  4.00000 : wrong
>   #declare F = function {prod(n, 1,2, n/1)}   =>  4.00000 : wrong
>   #declare F = function {prod(n, 1,2, (n+0))} =>  4.00000 : wrong
> 

So we learn from this that the sum function is just not to be trusted here.
I guess that I shall be needing to use something else.
I thought that I could have gnuplot plot the function output to a table and 
then post-process the table.  There the values would be given as point 
triples.  Then to pull those into povray somehow.  I looked into this and 
it looked as though the bicubic patch would work but then no and then I 
thought about the mesh or mesh2 object.  I just do not have experiance with 
this, what object is reccommemded for this kind of work.  I have searched 
the internet for examples of people doing scientific plotting with povray 
in this capcity and did not come up with much of anything.

I guess that I would list the sum and prod functions as buggy, I will submit 
a bug report to the pov gods.  Thanks for thinking to do that.

Justace

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