Create matrix using nested loops
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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.
采纳的回答
Mohammad Abouali
2014-9-18
编辑：Mohammad Abouali
2014-9-18
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.
更多回答（1 个）
Jos (10584)
2014-9-18
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 个评论
Joseph Cheng
2014-9-18
some additional help is that you can use sind() and cosd() to stay with degrees and not convert to radians. And if you want 2x5 (2 rows and 5 columns) then switch the j and 1/2 in the Y(j,#) around so it reads Y( row 1, column j) = sin(tmp);
Duffy Duck
2014-9-18
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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