integration with limits using an array

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James Keiser 2022-10-6

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https://ww2.mathworks.cn/matlabcentral/answers/1818870-integration-with-limits-using-an-array

评论： the cyclist 2022-10-6

I am trying to integrate an equation and it works when I do not have limits but when I add them it does not work.

u_wake is a 1x56 array, rho is a constant and 0.07 and 0.13 are the limit boundaries.

This works when I use this:

Drag = rho*trapz(u_wake.*(21.15-u_wake));

But not when I do this:

Drag = rho*trapz(u_wake.*(21.15-u_wake),0.07,0.13);

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James Keiser 2022-10-6

编辑：James Keiser 2022-10-6

I cannot upload the data because it is 56 files and I am only allowed to upload 10. The data is 56 numbers all below 21.15 .

The error code is:

Error in wake_scan_sample (line 35)

Drag = rho*trapz(u_wake.*(21.15-u_wake),0.07,0.13);

the cyclist 2022-10-6

It's unclear to me why you can't just upload u_wake, which is just a 1x56 vector.

Also, that is not the complete error message, which I am guessing looks something more like ...

Error using matlab.internal.math.getdimarg

Dimension argument must be a positive integer scalar within indexing range.

Error in trapz>getDimArg (line 90)

dim = matlab.internal.math.getdimarg(dim);

Error in trapz (line 36)

dim = min(ndims(y)+1, getDimArg(dim));

Error in wake_scan_sample (line 35)

Drag = rho*trapz(u_wake.*(21.15-u_wake),0.07,0.13);

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Answer 1

the cyclist 2022-10-6

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1818870-integration-with-limits-using-an-array#answer_1068110

Looking at the documentation for trapz, it doesn't seem like the syntax you are trying to use is valid.

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James Keiser 2022-10-6

What would recommend to fix the syntax?

the cyclist 2022-10-6

在 MATLAB Online 中打开

I assume that u_wake is the "y" value of the integral. Are 0.07 and 0.13 the endpoints of the "x" value? Are the values of u_wake at evenly spaced points along x? Then

Drag = rho*trapz(linspace(0.07,0.13,length(u_wake)),u_wake.*(21.15-u_wake));

should calculate what you want. For example,

% I just made up some u_wake and rho data
u_wake = sort(rand(1,56));
rho = 1;
Drag = rho*trapz(linspace(0.07,0.13,length(u_wake)),u_wake.*(21.15-u_wake))
Drag = 0.5618