how to create 1*101 of some integer array?
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Hi,
Very basic que: I would like to have 1*101 of -4 array. I have to solve an integral numerically
int_0^x -4 dx;
My code is like:
x= linspace(0,1,0.01);
A = zeros(1,101);
..
cumtrapz(x,-4*A);
But the command prompt shows all zeros for cumtrapz which is certainly not.
If I just use :
cumtrapz(x,-4);
it says matrix dimensions must agree. How can I create this array?
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Accepted Answer
Mohammad Abouali
on 5 Apr 2015
Edited: Mohammad Abouali
on 5 Apr 2015
Yo have:
A = zeros(1,101);
and then later you have
cumtrapz(x,-4*A);
all elements of A are zero so -4*A is going to be still zero.
change A=zeros(1,101) to A=ones(1,101)
Also as imageAnalyst said, the third argument for linspace is not the spacing so you need to change the code to something like this
x=linspace(0,1,101);
A=ones(1,101);
cumtrapz(x,-4*A);
By the way, are you sure you want to use cumtrapz()? don't you want the output of trapz()?
2 Comments
Mohammad Abouali
on 6 Apr 2015
Both trapz(x,y) and cumtrapz(x,y) integrate between x and y for the entire domain.
Trapz gives you one number. But cumtrapz gives all the values from start to end.
So if x=xStart:dx:xEnd then trapz gives int_xStart^xEnd but cumtrapz will give an array the first one is for int_xStart^{xStart+dx) the second one is for int_xStart^{xStart+2dx} and the n-th number is for int_xStart^{xStart+n*dx}.
the last number of cumtrapz and trapz should be the same.
Both can be useful. just make sure which one is it that you want.
More Answers (1)
Image Analyst
on 5 Apr 2015
The third argument of linspace is the number of elements, not the increment between elements. Try this:
numberOfElements = 101; % Whatever you want
x= linspace(0, 1, numberOfElements);
A = zeros(1, numberOfElements);
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