Alternative for linspace?

Question

Sarah Gomez 2022-2-11

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1647500-alternative-for-linspace

评论： VBBV 2024-2-25

function [xvals, yvals]=A5fourier(L,nmax,numpoints)
%xvals=linspace(-L,L,numpoints);
for z=-0.1:0.001:0.1
    xvals=z;
end 
yvals=zeros(1,numpoints);
for i=1:numpoints
    for j=1:2:nmax
        yvals(i)=(4/pi)*(yvals(i)+(1/j)*sin(j*pi*xvals(i)/L));
        j=j+1;
    end
    i=i+1;
end

L in this function is 0.1, and numpoints is 200. I've been challenged to use a loop rather than linspace to create the same 200 equally spaced points. My current solution ruins my yvals part of the function returning an error "Index exceeds the number of array elements". How can I remedy linspace while mainting the rest of my function?

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Answer 1

DGM 2022-2-11

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https://ww2.mathworks.cn/matlabcentral/answers/1647500-alternative-for-linspace#answer_893615

编辑：DGM 2022-2-11

在 MATLAB Online 中打开

Why not just use the colon operator?

r = [-4 4];
n = 10;
x1 = linspace(r(1),r(2),n)
x1 = 1×10
   -4.0000   -3.1111   -2.2222   -1.3333   -0.4444    0.4444    1.3333    2.2222    3.1111    4.0000
x2 = r(1):range(r)/(n-1):r(2)
x2 = 1×10
   -4.0000   -3.1111   -2.2222   -1.3333   -0.4444    0.4444    1.3333    2.2222    3.1111    4.0000

This can definitely be simplified. The iterator in a for-loop doesn't need to be incremented.

yvals=zeros(1,numpoints);
for i=1:numpoints
    for j=1:2:nmax
        yvals(i)=(4/pi)*(yvals(i)+(1/j)*sin(j*pi*xvals(i)/L));
        % j=j+1; % this doesn't do anything
    end
    % i=i+1; % this doesn't do anything
end

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VBBV 2024-2-25

在 MATLAB Online 中打开

@Sarah Gomez, if your question involves, to use the for loops /other loops to create linearly spaced points, then this could be one option to do so, however, there are several redundant lines of code in your function whcih @DGM pointed out. Further, ihe simplest altrenative would be to use the colon : operator which also was mentioned by @DGM

[xvals yvals] = A5fourier(0.1,200,200)
xvals = 1×201
   -0.1000   -0.0990   -0.0980   -0.0970   -0.0960   -0.0950   -0.0940   -0.0930   -0.0920   -0.0910   -0.0900   -0.0890   -0.0880   -0.0870   -0.0860   -0.0850   -0.0840   -0.0830   -0.0820   -0.0810   -0.0800   -0.0790   -0.0780   -0.0770   -0.0760   -0.0750   -0.0740   -0.0730   -0.0720   -0.0710
yvals = 1×200
1.0e+10 *

   -0.0000   -0.4436   -0.8361   -1.1547   -1.4027   -1.5940   -1.7426   -1.8596   -1.9533   -2.0295   -2.0925   -2.1452   -2.1898   -2.2280   -2.2609   -2.2896   -2.3148   -2.3370   -2.3567   -2.3743   -2.3901   -2.4043   -2.4171   -2.4286   -2.4392   -2.4487   -2.4575   -2.4654   -2.4727   -2.4794
linspace(-0.1,0.1,200)
ans = 1×200
   -0.1000   -0.0990   -0.0980   -0.0970   -0.0960   -0.0950   -0.0940   -0.0930   -0.0920   -0.0910   -0.0899   -0.0889   -0.0879   -0.0869   -0.0859   -0.0849   -0.0839   -0.0829   -0.0819   -0.0809   -0.0799   -0.0789   -0.0779   -0.0769   -0.0759   -0.0749   -0.0739   -0.0729   -0.0719   -0.0709
function [xvals, yvals]=A5fourier(L,nmax,numpoints)
%xvals=linspace(-L,L,numpoints);
% alternative to linspace using for loops !!! 
k = 1;
for z=-0.1:0.001:0.1
    xvals(k)=z;
    k = k+1;
end 
yvals=zeros(1,numpoints);
for i=1:numpoints
    for j=1:2:nmax
        yvals(i)=(4/pi)*(yvals(i)+(1/j)*sin(j*pi*xvals(i)/L));        
    end    
end
end