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matlabplotmatlab-figuresurface

Dissimilar results to the surface plot in MATLAB

>> x=0:0.001:720;
>> y=sind(x);
>> z=cosd(x);
>> surf(x,y,z);

I want to plot a surface using the above code i.e. x in X-axis, y is Y-axis, and z in Z-axis. I also programmed a FORTRAN code for the following purpose, created a csv file, and plotted it in origin. I am getting a result as this:

FORTRAN Result

However, in MATLAB, I am getting a similar idea when using:-

>> plot3(x,y,z)

as in this image:

MATLAB Result

but it's not a surface (for obvious reasons).

When using the surf command, I am also getting an error saying:

Z must be a matrix, not a scalar or vector.

What could be the possible problem with my code?

Solution

  • Using surf requires Z to be a matrix. This is fixed easily with functions like meshgrid (also useful is griddata).

    Using meshgrid makes using surf very accessible.

    But both Z and Y are just functions of X so I'm unable to explain why your plot Z-value would change with both X and Y. From the analytical (mathematical) equations you've listed, the Z-value should be constant in the Y-dimension.

    stepsize = 1;     % use 10 for cleaner look
x = 0:stepsize:720;
y = sind(x);
[X,Y] = meshgrid(x,y);
Z = cosd(X);

surf(X,Y,Z)

    Surface plot

    Notice that the contour lines are straight & parallel in the Y dimension (using surfc(X,Y,Z)). Surface plot with contours shown beneath

    Another method is to loop through elements of x (indexed by i) and y (indexed by j) where both x and y (vectors) to calculate Z(i,j) where Z is a matrix. Due to default assignment for rows & columns, this method requires transposing the Z matrix such as surf(X,Y,Z.').

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