Create matrix using nested loops

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Duffy Duck
Duffy Duck am 18 Sep. 2014
Kommentiert: Joseph Cheng am 18 Sep. 2014
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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Mohammad Abouali
Mohammad Abouali am 18 Sep. 2014
Bearbeitet: Mohammad Abouali am 18 Sep. 2014
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.
  2 Kommentare
Andrei Bobrov
Andrei Bobrov am 18 Sep. 2014
Y = [sind(Theta);cosd(Theta)];
Duffy Duck
Duffy Duck am 18 Sep. 2014
Thank you very much !

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Weitere Antworten (1)

Jos (10584)
Jos (10584) am 18 Sep. 2014
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.
  3 Kommentare
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Duffy Duck
Duffy Duck am 18 Sep. 2014
Thank you very much !
Joseph Cheng
Joseph Cheng am 18 Sep. 2014
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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