the fsurf produce incorrect plotting?

Hi,

When I use [syms]+[fsurf]

it seems not produce correct answer:

syms T P
G=T*log(P);
fsurf(G,[298 500 10^(-10) 10])

it can be easily checked that it doesn't produce correct plotting by any analytical calculation

So why is that?

Answer 1

[Asvin Kumar]

The output by fsurf in the example given is being plotted for P in the range of 298 – 500 and T in the range of 10^(-10) – 10. This behaviour is observed because fsurf maps the values in the xyinterval argument to the symbolic variables in G as listed in:

symvar(G) 

One simple workaround for this would be to replace [298 500 10^(-10) 10] with [10^(-10) 10 298 500].

Another approach would be to use symfun as follows:

syms T P
G= symfun(T*log(P),[T P]); 
fsurf(G,[298 500 10^(-10) 10]); 

For more details have a look at:

https://www.mathworks.com/help/symbolic/fsurf.html?s_tid=doc_ta#buzhv1f-2 (3rd Description)

https://www.mathworks.com/help/symbolic/find-symbolic-variables-in-expressions-functions-matrices.html

https://www.mathworks.com/help/symbolic/symfun.html