Create matrix using nested loops

Question

Duffy Duck 2014-9-18

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评论： Joseph Cheng 2014-9-18

Hi everyone, I would like to create a 2x5 matrix. Row 1 will be the sin(x) and Row 2 the cos(x). Each column will be the values of x being 0, 90, 180, 270, 360.

I do not seem to get it right. Can anyone please direct me to my mistake? I do not need a solution to my assignment, I just need some guidance.

for j=0:4
    j=j+1
      for i=0:90:360
      Y(1,j)=sin(i)
      Y(2,j)=cos(i)
       end
  end

Any help is appreciated.

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Answer 1

Mohammad Abouali 2014-9-18

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https://ww2.mathworks.cn/matlabcentral/answers/155364-create-matrix-using-nested-loops#answer_152171

编辑：Mohammad Abouali 2014-9-18

在 MATLAB Online 中打开

Theta=[0, 90, 180, 270, 360];
Y=zeros(2,numel(Theta))
Y(1,:)=sind(Theta);
Y(2,:)=cosd(Theta);

NOTE the "d" after sin and cos function.

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Andrei Bobrov 2014-9-18

在 MATLAB Online 中打开

Y = [sind(Theta);cosd(Theta)];

Duffy Duck 2014-9-18

Thank you very much !

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Answer 2

Jos (10584) 2014-9-18

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在 MATLAB Online 中打开

Note that

Indexing in ML starts at 1
You should rarely change the iterator inside the loop
sin and cos take radians, rather than degrees
do you really need a double loop?

Angles = [0 90 180 270] % angles in degrees
N = numel(Angles)
Y = nan(N,2) % pre allocation
for j=1:N
    tmp = Angles(j) * (pi/180)
    Y(j,1) = sin(tmp)
    Y(j,2) = cos(tmp)
end

Note that you can vectorise this.

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Duffy Duck 2014-9-18

Thank you very much !

Joseph Cheng 2014-9-18

also there is no need to do this in a loop. the sin and cos functions will accept arrays and perform the sin and cos on each index. so similarly how Jos has Angles you can go cos(angles) and have the cos of each individual index as a return.

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