# how to estimate/evaluate the integral of a constant value function?

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Jinquan Li on 23 Feb 2021
Commented: Jinquan Li on 23 Feb 2021
For example, f = 5, for 0<t<1, zero otherwise.
i tried the following code but it didn't work:
syms t
f = 10;
int(f)

Walter Roberson on 23 Feb 2021
Edited: Walter Roberson on 23 Feb 2021
syms t a b real
f = piecewise(0 < t & t < 1, 5, 0)
f =
int(f, t, a, b)
Warning: Unable to check whether the integrand exists everywhere on the integration interval.
ans =
Jinquan Li on 23 Feb 2021
thanks. this works. Now i have another question. What if i use numerical integration? Here is what i tried:
f1 = @(t) piecewise(0<t & t<1, 10, 0);
q = integral(f1,0,1)

Just Manuel on 23 Feb 2021
Try this:
syms t
f = 0*t + 10;
int(f);
Cheers Manuel
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Just Manuel on 23 Feb 2021
Edited: Just Manuel on 23 Feb 2021
you can't use piecewise in a numerical context. redefine your function as follows:
f = @(t) 5 .* (t > 0 & t < 1);
% then you can calculate numerical integral like this
integral(f, -1, 1)
Cheers
Manuel
Jinquan Li on 23 Feb 2021
Thanks a lot! this works!