MATLAB: Indentify spcific point of matrixs

MATLABmatrix

currently I have two matrix which is drag and thrust as you see below, and the number of two martix is going to be very close at some point, and I need to find out what the spcific number of drag and thrust when they are really close to each other, I have try to write the flowing function, but it only return the orginal matrix of thrust

function [maxSpeed,thrustDragVal] = maxSpeedThrustCalc(V, thrust, drag)

for difference = thrust – drag

if abs(difference) <= 0.01

maxSpeed = V;

thrustDragVal = thrust;

end

Best Answer

Hi Felix,

I see that the for loop condition is not correct. You can try the following

function [maxSpeed,thrustDragVal] = maxSpeedThrustCalc(V, thrust, drag)
for i = 1:length(thrust)
    difference = thrust(i) - drag(i);
    if abs(difference) <= 0.01 
        maxSpeed = V;
        thrustDragVal = thrust(i);
    end
end
end
% You mentioned that drag and thrust need to be known, but i am not sure why the output is set to maxSpeed
% You indicate the minimum difference, but why is the threshold placed as 0.01
% If both the above is same as what is said, you need to use the following code
difference = thrust - drag;
[m,i] = min(abs(difference)); % m is the minimum value and i is the index where minimum occurs
thrustVal = thrust(i);
dragVal = drag(i);

Hope this helps.

Regards,

Sriram

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function [maxSpeed,thrustDragVal] = maxSpeedThrustCalc(V, thrust, drag)
  i=find(abs(drag-thrust)<.1,1,'last');%not sure what tolerance you need
  maxSpeed = V(i);
  thrustDragVal = thrust(i);
end

MATLAB: How to plot a line graph from two for loops

If you want to do a simulation where you are stepping forward in time, I suggest saving the results of each timestep so when your simulation completes you have all the data.

In your example, you see to be recreating your data at the end in order to plot.

Note: my example is just to show you the structure I am suggesting

    % Model Parameters
        burnrate = 50; % kg/s
        fuel = 4000; % kg
        t = fuel / burnrate; % seconds
        a_thrust = + 20; % m/s^2

        a_gravity = -9.8; % m/s^2
        y_0 = 0; % m
        v_0 = 0; %m/s
    % Simulate each second:
    altitude = y_0;
    velocity = v_0;
    acceleration = 0;
    time = 0;
    % Simulate until rocket is below ground level
    while altitude >= 0
        time(end + 1) = time(end) + 1;
        % Change model behavior based on fuel
            if fuel > 0
                deltaFuel = burnrate;
                accel = a_thrust;
            else
                deltaFuel = 0;
                accel = a_gravity;
            end
        % Build vectors for each parameter at each timestep
            fuel = fuel - burnrate;
            acceleration(end + 1,1) = accel;
            velocity(end + 1,1) = velocity(end) + accel;
            altitude(end + 1,1) = altitude(end) + velocity(end);
    end
    % Use logical indexing to select the data corresponding to a positive
    % vertical velocity
        % Some benefits of this approach are that you can do additional
        % math on your results. For example, you could find the points with
        % positive acceleration as follows (if you didn't already have an
        % acceleration vector)
        posAccelIndex = diff(velocity)>0; % NOTE: this vector is 1 line shorter than the model!
        posAccelIndex = [true; posAccelIndex]; % Include the initial condition
        % Since you do have that parameter, you can use simple logical
        % indexing:
        posAccelIndex = acceleration >= 0;
    % Print some output - use the vectors you built in the model
    disp(sprintf('Altitude reached: %f meters', max(altitude)));
    disp(sprintf('Velocity at impact: %f m/s', velocity(end)));
    % Plot your results using logical indexing to color code and set the legend
    figure;
    subplot(1,2,1)
        hold on;
        plot(time(posAccelIndex),  velocity(posAccelIndex),  'r', 'displayname', 'Powered');
        plot(time(~posAccelIndex), velocity(~posAccelIndex), 'b', 'displayname', 'Freefall');
        title('Vehicle Velocity (in m/s)')
        legend('show')
    subplot(1,2,2)
        hold on;
        plot(time(posAccelIndex),  altitude(posAccelIndex),  'r', 'displayname', 'Powered');
        plot(time(~posAccelIndex), altitude(~posAccelIndex), 'b', 'displayname', 'Freefall');
        title('Vehicle Altitude (in m)')
        legend('show')

Hopefully this helps!

Best Answer

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MATLAB: How to choose the spcific intersection of two arry

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