In Matlab: How to plot the function versus , where ? I have obtaind the an array of values for through some (long) numerical calculation, for an array of values . The function has an analytic expression: . My question is how to plot , which is a function of defined by this integral over another function of ? (The ``" is not the problem, of course this can just be set to some large constant, e.g., or , maybe?) *To emphasize: I know how this can be done using a loop for each value of : for every , I can calculate P(x)=trapz(y,f(y)W(x,y)) (~not written in Matlab code). But, can this be done without a loop?

Matlab: How to plot the function $P(x)$ versus $x$, where $P(x)=\int_0^\infty f(y)W(x,y)dy$?

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Erez 2022-6-10

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https://ww2.mathworks.cn/matlabcentral/answers/1738095-matlab-how-to-plot-the-function-p-x-versus-x-where-p-x-int_0-infty-f-y-w-x-y-dy

评论： Walter Roberson 2022-7-14

In Matlab:

How to plot the function

versus x, where

I have obtaind the an array of N values for

through some (long) numerical calculation, for an array of N values y.

The function

has an analytic expression:

My question is how to plot

, which is a function of x defined by this integral over another function of y?

(The ``∞" is not the problem, of course this can just be set to some large constant, e.g.,

, maybe?)

*To emphasize: I know how this can be done using a loop for each value of x : for every x, I can calculate P(x)=trapz(y,f(y)W(x,y)) (~not written in Matlab code).

But, can this be done without a loop?

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Erez 2022-6-13

@Torsten @Image Analyst @Walter Roberson Guys, thanks for all the ideas, can you show please how to implemet them? -- I haven't been able to understand how to do it myself from the comments :) Maybe it is simple.. but not to me ;)

Torsten 2022-6-13

编辑：Torsten 2022-6-13

在 MATLAB Online 中打开

Follow Walter Roberson's hint :

y = (0:10:100).';
x = 3:6;
W = exp(-x.^2./y);
f = @(y)y.^2;
fy = repmat(f(y),1,numel(x));
result = trapz(y,fy.*W)
result = 1×4
1.0e+05 *

    2.9353    2.6553    2.3400    2.0112

Can you take it from here ?

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回答（1 个）

David Hill 2022-6-13

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1738095-matlab-how-to-plot-the-function-p-x-versus-x-where-p-x-int_0-infty-f-y-w-x-y-dy#answer_984765

在 MATLAB Online 中打开

y=1:.01:5;
x=0:.01:7;
[X,Y]=meshgrid(x,y);
W=exp(-X.^2./Y);
f=y.^2;%as an example
I=trapz(W.*f')/.01;%each column of I is the integral at each corresponding x value