# What are the valid operations on an fespace?
**URL:** https://community.freefem.org/t/what-are-the-valid-operations-on-an-fespace/2978
**Category:** General Discussion
**Created:** [February 20, 2024, 2:29am UTC](https://community.freefem.org/t/what-are-the-valid-operations-on-an-fespace/2978 "2024-02-20T02:29:40Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@glenwheeler](https://community.freefem.org/u/glenwheeler)
#### Post date: [February 20, 2024, 2:29am UTC](https://community.freefem.org/t/what-are-the-valid-operations-on-an-fespace/2978/1 "2024-02-20T02:29:40Z")
Hi everyone!
I’m a total beginner at using FreeFEM++. I wanted to calculate the negative part of an fespace X by using
max(-X, 0.0);
but it didn’t work. Instead, I used a loop like this:
for(int i = 0; i \< Vh.ndof; ++i) {
X[i] = max(-X[i], 0.0);
}
which worked. I understand that max doesn’t apply to fespaces. But some operations do apply. I tried searching the documentation but I couldn’t find a list of what are valid operations. Can anyone help?
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### Author:  [@julienG](https://community.freefem.org/u/julienG)
#### Post date: [February 20, 2024, 4:33am UTC](https://community.freefem.org/t/what-are-the-valid-operations-on-an-fespace/2978/2 "2024-02-20T04:33:25Z")
You can get max an min of the array of you degrees of freedom like this
> cout \<\< X.min\<\< " "\<\< X.max \<\
### Author:  [@frederichecht](https://community.freefem.org/u/frederichecht)
#### Post date: [February 22, 2024, 9:13am UTC](https://community.freefem.org/t/what-are-the-valid-operations-on-an-fespace/2978/3 "2024-02-22T09:13:01Z")
first X is not a fespace but a function in fespace.
if you call Vh the fespace, then X is defined by
Vh X;
then
Vh X0 = max(-X,0.0); // work !
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### Author:  [@glenwheeler](https://community.freefem.org/u/glenwheeler)
#### Post date: [February 23, 2024, 1:37am UTC](https://community.freefem.org/t/what-are-the-valid-operations-on-an-fespace/2978/4 "2024-02-23T01:37:16Z")
Hi Frederic,
Yes, of course, the code looks like
fespace Vh(Th, P1);
Vh X;
OH I see, so
X = max(-X,0);
does not work, but
X0 = max(-X,0);
does. I just wanted to replace X, but I need an intermediate point.
So “max” is a valid operation. Great! Do you know where the others are listed…?