Interpolating matrices with 2 variables and 1 dependent value - matlab

Question

I'm analyzing an induction motor, varying the frequency and absolute value of the stator current. Since the FEM-Tool only works with a current input, I need to vary the current over the frequency to obtain current-values of constant torque for each frequency.
To generate a mesh, I use 2 for-loops:
The outer loop sets the current.
The inner loop varies the frequency with said current, gets the machine's torque and finally, the matrices are appended adding the current stator-current, frequency and torque each in separate matrices. Plotted it looks like this:
Example of the plot using the raw data
For the plot I used smaller, more imprecise matrices and rather arbitrary values:
I_S = [ 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 ];
fre = [ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 ];
tor = [ 0 0.1 0.3 0.5 0.7 1 1.5 2 2.6 3.3 0 1.1 1.3 1.5 1.7 2 2.5 3 3.6 4.3 0 2.1 2.3 2.5 2.7 3 3.5 4 4.6 5.3 ];
While tor is shown as the colormap in the plot. Each matrix has a length of 30.
One simulation needs about 20-30 seconds. Thus, to get a precise mesh, the FEM-tool needs several hours to generate.
I would like to interpolate the spaces in between the known ones.
It seems that either the way of creating the matrices is the problem or the interp*...-functions of Octave/MATLAB simply don't work for this kind of interpolation.
Is there a way to achieve a mesh/grid-like interpolation from this type of matrices? I found many examples with x,y as variables and z as a math-function but rarely 3 linear/non-linear matrices.

Answer 1

Your data need to be in a meshgrid form, that is 2D:
// Known data
current = [0:2];
frequency = [0:9];
[current2D, frequency2D] = meshgrid(current,frequency);
torque2D = [ 0 0.1 0.3; 0.5 0.7 1; 1.5 2 2.6; 3.3 0 1.1; 1.3 1.5 1.7; 2 2.5 3; 3.6 4.3 0; 2.1 2.3 2.5; 2.7 3 3.5; 4 4.6 5.3 ];
// Interpolated data
currentToInterpolate = [0.5 1.5];
frequncyToInterpolate = [0.5 : 8.5];
[currentToInterpolate2D, frequencyToInterpolate2D] = meshgrid(currentToInterpolate,frequncyToInterpolate);
interpolatedTorque2D = interp2(current2D,frequency2D,torque2D,currentToInterpolate2D,frequencyToInterpolate2D);