Why do I keep getting this error? Error using surf Z must be a matrix, not a scalar or vector.

Moment=zeros(); ki=pi/180; kinc=pi/180; kf=pi; ji=5; jinc=5; jf=100;
for k=ki:kinc:kf
    for j=ji:jinc:jf
        h=sin(k)
        g= cos(k)
        Moment (j/jinc,:) = 1800 + j * h * 39 + j * g * 6
    end
end
%k is theta j is force
[k,j] = meshgrid(ki:kinc:kf,ji:jinc:jf);
figure
surf(k,j,Moment)
xlabel('0 (degrees)'); ylabel('Force (lbs)'); zlabel('Moment (lbs-ft)')

[VBBV]

one way to modify your code is below

ki=pi/180; kinc=pi/180; kf=pi; ji=5; jinc=5; jf=100;
Moment=zeros(); 
% initialize a counter
K = 1;

for k=ki:kinc:kf
    for j=ji:jinc:jf
        h(K) = sin(k);  % make h as array
        g(K) = cos(k);  % make g as array
        Moment (j/jinc,1:K) = 1800 + (j) * h * 39 + (j) * g * 6;
    end
    K = K+1; % increment in for loop
end
% plot using surf
[k,j] = meshgrid(ki:kinc:kf,ji:jinc:jf);
figure
surf(k,j,Moment)
xlabel('0 (degrees)'); ylabel('Force (lbs)'); zlabel('Moment (lbs-ft)')

[MyRanda]

When I do this I get an error.

[Walter Roberson]

K=1;

so 1:K is 1:1 so you are assigning to Moment(something, 1) which is creating a vector, not a 2D array.

[MyRanda]

ki=pi/180; kinc=pi/180; kf=pi; ji=5; jinc=5; jf=100;
Moment=zeros(); 
% initialize a counter
K = 1;
for k=ki:kinc:kf
    for j=ji:jinc:jf
        h(K) = sin(k);  % make h as array
        g(K) = cos(k);  % make g as array
        Moment (j/jinc,1:K) = 1800 + (j) * h * 39 + (j) * g * 6;
    end
    K = K+1; % increment in for loop
end
% plot using surf
[k,j] = meshgrid(ki:kinc:kf,ji:jinc:jf);
figure
surf(k,j,Moment)
xlabel('0 (degrees)'); ylabel('Force (lbs)'); zlabel('Moment (lbs-ft)')

[MyRanda]

this is what I have and I am getting an error.

[Walter Roberson]

Your posted code is running.

[MyRanda]

I am getting an error on my computer.

[Walter Roberson]

Make sure you clear your variables. You probably have a variable the wrong size sitting around.

[VBBV]

@Walter Roberson +1

[Adam Danz]

Note, duplicate

https://www.mathworks.com/matlabcentral/answers/1944829

Answer 1

[Cris LaPierre]

Because your variable moment is a vector not a matrix. moment must be the same size as k and j (the ones resulting from your meshgrid operation).

[Walter Roberson]

In particular. 1800 + j * h * 39 + j * g * 6 is a scalar result, so Mement(j/jinc, :) would be assigned only a single value.

Answer 2

[Walter Roberson]

ki=pi/180; kinc=pi/180; kf=pi; ji=5; jinc=5; jf=100;
[k,j] = meshgrid(ki:kinc:kf,ji:jinc:jf);
h = sin(k);
g = cos(k);
Moment = 1800 + j .* h .* 39 + j .* g .* 6;

surf(k, j, Moment);
xlabel('0 (degrees)'); ylabel('Force (lbs)'); zlabel('Moment (lbs-ft)')

[MyRanda]

my assignment requires a nested loop. How would I do that?

[Walter Roberson]

Do the meshgrid first. Then

for ridx = 1 : number of rows
    for cidx = 1 : number of columns
       output_variable(ridx,cidx) = calculation in terms of variables indexed at (ridx,cidx);
    end
end