HELP!!! mapping with matrices

I have a peculiar problem and I've hit a massive wall. I am modeling driveline efficiencies and have a matrix with different engine efficiencies depending on torque and engine speed. I didn't know how to do this so I manually created a matrix with efficiency values for given ranges of torque and speed. For example, one row could be a specific range of speed (100-200 rpm) and each entry in that row is an efficiency corresponding to different ranges of torque (say 40-50 Nm, 50-60 Nm, etc,).

So I have a big bunch of efficiencies in a 21x8 matrix.

Now, I also have arrays for torque (vs. time) and speed (vs. time) and thus for POWER (vs. time). I now need to map each power entry to its corresponding efficiency, which depends on its torque and speed values at that time interval (to a specific entry in the efficiency map matrix). I don't know how to tell MATLAB to do so... Unless I create a massive LOOP with thousands os IFs...)

Please any help appreciated!

Answer 1

[nick]

Hello Yago,

To map each power entry to its corresponding efficiency based on torque and speed values, you can use 'find' function as shown below:

% Example efficiency matrix (21x8)
efficiencyMatrix = rand(21, 8);
torqueBins = [40, 50, 60, 70, 80, 90, 100, 110, 120]; %  torque bin edges
speedBins = [100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200]; % Example speed bin edges

% Example torque and speed arrays 
torqueArray = [45, 55, 65, 75, 85, 95, 105, 115];
speedArray = [150, 250, 350, 450, 550, 650, 750, 850]; 
efficiencyArray = zeros(size(torqueArray));

% Function to find bin index
findBinIndex = @(value, bins) find(value >= bins(1:end-1) & value < bins(2:end), 1);

% Map each torque and speed value to the corresponding efficiency
for i = 1:length(torqueArray)
    torqueIdx = findBinIndex(torqueArray(i), torqueBins);
    speedIdx = findBinIndex(speedArray(i), speedBins);
    
    if ~isempty(torqueIdx) && ~isempty(speedIdx)
        efficiencyArray(i) = efficiencyMatrix(speedIdx, torqueIdx);
    else
        efficiencyArray(i) = NaN; 
    end
end

disp('Torque values:');

Torque values:

disp(torqueArray);

    45    55    65    75    85    95   105   115

disp('Speed values:');

Speed values:

disp(speedArray);

   150   250   350   450   550   650   750   850

disp('Mapped Efficiency values:');

Mapped Efficiency values:

disp(efficiencyArray);

    0.9749    0.6528    0.4996    0.4454    0.4635    0.0423    0.0676    0.1024

Kindly refer to the documentation by executing the following command in MATLAB Command Window to know more about 'find' function :

doc find