MATLAB: Unable to perform assignment because the left and right sides have a different number of elements. Line “u(i) = u(I+1) + acceleration * dt” seems to be the problem.

error

How can I fix this code to run and print the table? 
% Default parameter values
mass = 1;
Spring = 200;
Initial = 1;
staticf = 0.2;
dynamicf = 0.1;
Period = 7;
dt = 0.01;
angle = 30;
g = 9.81; 
i = 3;
u(i-2) = 0;
u(i-1) = 0;
displacement_data(i-1) = 0;
    
for time = 0:dt:Period
        
        if u(i-1) > 0
            multiplier = -1;
        else
            multiplier = 1;
        end
        
        if u(i-2) <= 0 && u(i-1) >= 0
            fres = (mass*g*(sind(angle)) - (staticf*cosd(angle)));
        elseif (u(i-2) >= 0 && u(i-1) >= 0 && displacement_data(i-1) < Initial) || (u(i-2) < 0 && u(i-1) < 0 && displacement_data(i-1) < Initial)
            fres = mass*g*(sind(angle) + multiplier*(dynamicf*cosd(angle)));
        elseif u(i-2) >= 0 && u(i-1) <= 0
            fres = mass*g*(sind(angle) + staticf*cosd(angle)) - spring*(displacement_data(i-1) - Initial);
        elseif u(i-2) >=0 && u(i-1) >= 0 && displacement_data(i-1) >= Initial || u(i-2) < 0 && u(i-1) < 0 && displacement_data(i-1) >= Initial
            fres = mass*g*(sind(angle) + multiplier*(dynamicf*cosd(angle))) - spring*(displacement_data(i-1) - Initial);
        end
        
        acceleration = fres/mass;
        
        u(i) = u(i-1) + (acceleration * dt);
        displacement_data(i) = displacement_data(i-1) + u(i) * dt; 
            
        i = i + 1; 
        
        
    end
    
    
   fprintf('displacement\t\tacceleration\t\ttime\t\tvelocity\n')
        for(i=3: length(u-3))
            fprintf('%.4f\t\t%.4f\t\t%.4f\t\t%.4f\n', displacement_data(i-1), acceleration_data(i-1), time_data(i), u(i-1));
   
        end

Best Answer

When I ran your code, I got the same error. I tracked it down to your use of ‘spring’ as a variable name, as well as noting that in your ‘fres’ assignments that use it, you did not initially capitalise it.. This is actually the name of a colormap, so was creating a (64x3) matrix for your variable, and that was throwing the error. I corrected it to ‘Spring’ everywhere, and still got the error. What I find interesting is that as a general rule, MATLAB is case-sensitive, so ‘Spring’ and ‘spring’ should not be the same. (I am running this on R2019a.) I finally changed it to ‘SpringK’ everywhere, and the error disappeared.
The changes are: 
SpringK = 200;
and:
    if u(i-2) <= 0 && u(i-1) >= 0
        fres = (mass*g*(sind(angle)) - (staticf*cosd(angle)));
    elseif (u(i-2) >= 0 && u(i-1) >= 0 && displacement_data(i-1) < Initial) || (u(i-2) < 0 && u(i-1) < 0 && displacement_data(i-1) < Initial)
        fres = mass*g*(sind(angle) + multiplier*(dynamicf*cosd(angle)));
    elseif u(i-2) >= 0 && u(i-1) <= 0
        fres = mass*g*(sind(angle) + staticf*cosd(angle)) - SpringK*(displacement_data(i-1) - Initial);
    elseif u(i-2) >=0 && u(i-1) >= 0 && displacement_data(i-1) >= Initial || u(i-2) < 0 && u(i-1) < 0 && displacement_data(i-1) >= Initial
        fres = mass*g*(sind(angle) + multiplier*(dynamicf*cosd(angle))) - SpringK*(displacement_data(i-1) - Initial);
    end
We are left with one error: 
Undefined function or variable 'acceleration_data'.
    fprintf('%.4f\t\t%.4f\t\t%.4f\t\t%.4f\n', displacement_data(i-1), acceleration_data(i-1),
    time_data(i), u(i-1));
I defer to you to solve that.
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