In an assignment A(I) = B, the number of elements in B and I must be the same.

In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in step (line 18) dy(3) = 0.1e1 / l ^ 2 / (-cos(y(2)) ^ ......

%% the main first function function xc = totalmotion (q1_0, q2_0, dq1_0, dq2_0) global_constants; global M; % hip mass global m; % foot mass global l; % leg length global r; % the slop angle

global g; % gravity acceleration global delta_t; % compute interval step global rad; rad = 180/pi; global Kp; % the proportional coefficient global Kd; % the differential coefficient global q2d; % the desired value of q2 tspan = [0:delta_t:2]; options = odeset('abstol',1e-13,'reltol',1e-13,'events',@collision); y0 = [q1_0 q2_0 dq1_0 dq2_0]; %%% initial state p(1) = M; p(2) = m; p(3) = r; p(4) = l; [t,y]=ode45(@step,tspan,y0,options,p);

      n=length(t);
    for i =1:n
    q1 = y(i,1); q2 = y(i,2);
                x_0 = 0;
                y_0 = 0;          
                x1 = x_0;%%%%calculate the spacial positions of the links.   
                y1 = y_0;
                xh = x1 + l * sin(-q1 + r);
                yh = y1 + l * cos(-q1 + r);
                x2 = double(-l * sin(-q2 - q1 + r) + x1 + l * sin(-q1 + r));
                y2 = double(-l * cos(-q2 - q1 + r) + y1 + l * cos(-q1 + r));

    xc = (M * (x1 + l * sin(-q1 + r)) + m * (-l * sin(-q2 - q1 + r) + x1 + l * sin(-q1 + r))) / (M + 0.2e1 * m);

    end

end

%%% the second function function dy = step(t,y,p) M = p(1); m = p(2); r = p(3); l = p(4);

        dy = zeros(4,1);
        dy(1) = y(3);
        dy(2) = y(4);
        dy(3) = 0.1e1 / l ^ 2 / (-cos(y(2)) ^ 2 * m + M + m) * (-0.2e1 * sin(y(2)) * y(3) * y(4) * l ^ 2 * m - y(4) ^ 2 * sin(y(2)) * l ^ 2 * m - M * sin(-y(1) + r) * g * l - sin(-y(1) + r) * g * l * m + sin(-y(2) - y(1) + r) * m * g * l) + 0.1e1 / l ^ 2 * (cos(y(2)) - 0.1e1) / (-cos(y(2)) ^ 2 * m + M + m) * (Kp * (q2d - y(2)) - Kd * y(4) + sin(y(2)) * y(3) ^ 2 * l ^ 2 * m + sin(-y(2) - y(1) + r) * m * g * l);
        dy(4) = 0.1e1 / l ^ 2 * (cos(y(2)) - 0.1e1) / (-cos(y(2)) ^ 2 * m + M + m) * (-0.2e1 * sin(y(2)) * y(3) * y(4) * l ^ 2 * m - y(4) ^ 2 * sin(y(2)) * l ^ 2 * m - M * sin(-y(1) + r) * g * l - sin(-y(1) + r) * g * l * m + sin(-y(2) - y(1) + r) * m * g * l) + 0.1e1 / l ^ 2 * (-0.2e1 * cos(y(2)) * m + M + 0.2e1 * m) / m / (-cos(y(2)) ^ 2 * m + M + m) * (Kp * (q2d - y(2)) - Kd * y(4) + sin(y(2)) * y(3) ^ 2 * l ^ 2 * m + sin(-y(2) - y(1) + r) * m * g * l);

end Thanks for your help.

Answer 1

[Star Strider]

I cannot follow what you are doing, and I cannot run your code.

However, the most likely problem is that you need to vectorize your code, since otherwise MATLAB will interpret multiply, divide, and exponentiation operations as matrix rather than element-wise array operations. That means using the ‘dot operator’, substituting ‘.*’ for ‘*’, ‘./’ for ‘/’, and ‘./’ for ‘^’.

Use the vectorize (link) fiunction, and see the documentation on Array vs. Matrix Operations (link) for details.

[Qiaoli Ji]

Thanks for answering. I want to compute motion equation using ode45.

[t,y]=ode45(@step,tspan,y0,options,p);

% y0 is row vector,p is constant,step function is motion equation

 function dy = step(t,y,p)

1. dy = zeros(4,1);
2. dy(1) = y(3);
3. dy(2) = y(4);
4. dy(3) = 0.1e1 / l ^ 2 / (-cos(y(2)) ^ 2 * m + M + m) * (-0.2e1 * sin(y(2)) * y(3) * y(4) * l ^ 2 * m - y(4) ^ 2 * sin(y(2)) * l ^ 2 * m - M * sin(-y(1) + r) * g * l - sin(-y(1) + r) * g * l * m + sin(-y(2) - y(1) + r) * m * g * l) + 0.1e1 / l ^ 2 * (cos(y(2)) - 0.1e1) / (-cos(y(2)) ^ 2 * m + M + m) * (Kp * (q2d - y(2)) - Kd * y(4) + sin(y(2)) * y(3) ^ 2 * l ^ 2 * m + sin(-y(2) - y(1) + r) * m * g * l);
5. dy(4) = 0.1e1 / l ^ 2 * (cos(y(2)) - 0.1e1) / (-cos(y(2)) ^ 2 * m + M + m) * (-0.2e1 * sin(y(2)) * y(3) * y(4) * l ^ 2 * m - y(4) ^ 2 * sin(y(2)) * l ^ 2 * m - M * sin(-y(1) + r) * g * l - sin(-y(1) + r) * g * l * m + sin(-y(2) - y(1) + r) * m * g * l) + 0.1e1 / l ^ 2 * (-0.2e1 * cos(y(2)) * m + M + 0.2e1 * m) / m / (-cos(y(2)) ^ 2 * m + M + m) * (Kp * (q2d - y(2)) - Kd * y(4) + sin(y(2)) * y(3) ^ 2 * l ^ 2 * m + sin(-y(2) - y(1) + r) * m * g * l);

[Star Strider]

My pleasure.

You have to vectorize your equations, as I demonstrated. I cannot do this for you.

Answer 2

[Image Analyst]

You probably need to use the "dot" versions of * / ^ etc.

Put a dot/period before each mathematical operator, to do element-by-element operation instead of a matrix operation, and see how that goes.

[Qiaoli Ji]

sorry, I do not understand your meaning that 'put dot'. Could you show me an example? Thanks.

[Image Analyst]

Instead of

dy(3) = 0.1e1 / l ^ 2 / (-cos(y(2)) ^ 2 * m + M + m) * (-0.2e1 * sin(y(2)) * y(3) * y(4) * l ^ 2 * m - y(4) ^ 2 * sin(y(2)) * l ^ 2 * m - M * sin(-y(1) + r) * g * l - sin(-y(1) + r) * g * l * m + sin(-y(2) - y(1) + r) * m * g * l) + 0.1e1 / l ^ 2 * (cos(y(2)) - 0.1e1) / (-cos(y(2)) ^ 2 * m + M + m) * (Kp * (q2d - y(2)) - Kd * y(4) + sin(y(2)) * y(3) ^ 2 * l ^ 2 * m + sin(-y(2) - y(1) + r) * m * g * l);

try

dy(3) = 0.1e1 ./ l .^ 2 ./ (-cos(y(2)) .^ 2 .* m + M + m) .* (-0.2e1 .* sin(y(2)) .* y(3) .* y(4) .* l .^ 2 .* m - y(4) .^ 2 * sin(y(2)) .* l .^ 2 .........

etc.