Function returns scalar independent of input, but I need a matrix output

Question

DB 2022-3-30

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https://ww2.mathworks.cn/matlabcentral/answers/1684534-function-returns-scalar-independent-of-input-but-i-need-a-matrix-output

评论： DB 2022-3-31

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I have function handle f:

f = @(x)4.3206303272e-05.*x(1).^2+2.39837699915e-05.*x(2).^2

Where x is a

vector. I want to plot the mesh of this function, but each input returns a scalar. For example:

f([1 0]) =  4.3206e-05
f([1:4 5:7]) = 1.3914e-04
f3([rand(3) rand(3)]) = 5.3729e-06

How come, and how can I change this?

I came to a function handle because of this: Link

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Torsten 2022-3-30

编辑：Torsten 2022-3-30

Use arrayfun.

Or make a simple loop over the (x/y) combinations for which you want to evaluate the handle.

In the form given, the handle only accepts x to be a single vector, not a vector of vectors, since x(1) and x(2) are indexed.

DB 2022-3-31

I did not understand how to apply arrayfun. However, using a double for loop worked, and I got the mesh grid as desired! Thank you so much!

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Answer 1

KSSV 2022-3-30

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在 MATLAB Online 中打开

clc; clear all ;
f = @(x1, x2)4.3206303272e-05.*x1.^2+2.39837699915e-05.*x2.^2 ;
f(1,0) 
ans = 4.3206e-05
f([1:4]', [5:8]') 
ans = 4×1
    0.0006
    0.0010
    0.0016
    0.0022
f(rand(3,1),rand(3,1)) 
ans = 3×1
1.0e-04 *

    0.3743
    0.2474
    0.1337

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DB 2022-3-31

Yes but I have x as a 2x1 vector, and not x1 and x2, and I cannot seem to rewrite it to this. Furthermore, shouldn't it be possible with just a vector x? I mean it would take a lot of lines if you have a lot of variables.

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