# How to have use int() in a for loop?

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Seba.V on 22 Apr 2020
Answered: Walter Roberson on 22 Apr 2020
Hi there
The goal of this loop is to plot the value of A over a defined set of angles values al.
I believe the integrating function is giving the following error:
Error using symengine
Invalid argument.
Error in sym/int (line 162)
Is there a way to integrate a and gradually plot the values from an array?
I hope this makes sense
syms x
B=(pi-asin(1/2))
al=asin(1/2):0.001:B;
V=200*sin(x);
i=1;
for i=al(i)
F=double(subs(100*2*pi+int(V,x,al,B)-100*(B-al)))
Vdc=F/(2*pi);
A=(Vdc-100)/2
plot(al,A)
i=i+1
end

Walter Roberson on 22 Apr 2020
syms x
B=(pi-asin(1/2));
al=asin(1/2):0.001:B;
V=200*sin(x);
nal = numel(al);
A = zeros(size(al));
for i = 1 : nal
F=double(subs(100*2*pi+int(V,x,al(i),B)-100*(B-al(i))));
Vdc=F/(2*pi);
A(i)=(Vdc-100)/2;
end
plot(al, A)
This is rather slow (!!) The secret to doing int() in a for loop faster, is not to do int() inside a for loop. Instead, do the int() once before the loop, using a symbolic lower bound, and then subs() the numeric lower bound into that; you can do all the calculations in vectorized form.

KSSV on 22 Apr 2020
syms x
B=(pi-asin(1/2))
al=asin(1/2):0.001:B;
V=200*sin(x);
i=1;
for i=1:length(al)
I = double(int(V,x,al(i),B)) ;
F=((100*2*pi+I-100*(B-al(i))))
Vdc(i) = F/(2*pi);
A(i) =(Vdc-100)/2 ;
end