Getting an 'Array indices must be positive integers or logical values' error

In the given code, waypoints is a 3x3 matrix. The error comes in line 8.

persistent waypoints0 traj_time d0
    if nargin > 2
        d = waypoints(:,2:end) - waypoints(:,1:end-1);
        d0 = 2 * sqrt(d(1,:).^2 + d(2,:).^2 + d(3,:).^2);
        traj_time = [0, cumsum(d0)];
        waypoints0 = waypoints;
        
    else
        if t >= traj_time(end)
            t = traj_time(end);
        end
        t_index = find(traj_time > t,1) - 1;
        
        if (t_index == 0)
            t_index = 1;
        end
        if(t == 0)
            desired_state.pos = waypoints0(:,1);
        else
            scale = (t-traj_time(t_index)) / d0(t_index);
            index = [(t_index-1)*8+1:t_index*8];
            
        end
    end     

[KALYAN ACHARJYA]

Can you share the detail of other variables also, so that we can try on it?

[Aquatris]

Which line is line 8?

[Guillaume]

We really need the function line that this code goes into. The full text of the error message would be extremely useful as well. Also, tell us if it's when the persistent variables are initialised (i.e. nargin > 2) or when it's using them (nargin <= 2).

It's also not clear what the 3rd input would be. I can see just one input needed for initialisation (waypoints) and one input needed afterward (t).

[Orpheus]

Here is the original function

function [ desired_state ] = traj_generator(t, state, waypoints)
   
    % This function is called with variable number of input arguments.
    % During initialization, it will be called with arguments
    % trajectory_generator([], [], waypoints) and later, while testing, it will be
    % called with only t and state as arguments.
    %
    % t,state: time and current state (same variable as "state" in controller)
    % that is used for computing desired_state
    %
    % waypoints: The 3xP matrix listing all the points that have to be used in order
    % to generate the trajectory.
    
     
    
    
   function[t_m] =t_mat1(t)
                t_m=[1 t^1 t^2 t^3 t^4 t^5 t^6 t^7]';
            end
            function[t_m_dot] =t_mat2(t)
                t_m_dot = [0 1 2*t 3*t^2 4*t^3 5*t^4 6*t^5 7*t^6]';
            end
            function[t_m_ddot] =t_mat3(t)
                t_m_ddot = [0 0 2 6*t 12*t^2 20*t^3 30*t^4 42*t^5]';
            end 
    function[A,B]=pols_coef_retrn(n,wayp)
                A = zeros(8*n,8*n);
                B = zeros(8*n,1);
                p=1;
                l=1;
                for i=1:n
                    k=1;
                    l=p;
                    for j =1:8
                        if j==1
                            A(p,p)=1;B(p,1)=wayp(i);
                            A(p+1,p:p+7)=[1 1 1 1 1 1 1];B(p+1,1)=wayp(i+1);
                        end
                        p=p+1;
                        if j>=3
                            for theta = l+k:l+6
                                if i==1 && k<=4
                                    A(j,k+1)=1;
                                elseif i==n
                                    if k<=4
                                        A(l+j,:)= factorial(theta-l)/(factorial(k)^2);
                                    elseif k==5
                                        A(l+j,l+7)=1;
                                        A(l+j,8)=-1;
                                    elseif k==6
                                        A(l+j,l+6)=1;
                                        A(l+j,l-3)=-1;
                                        A(l+j,l+j)=-1;
                                    end
                                else
                                    A(l+j,theta)=-(factorial(theta-l)/(factorial(k)^2));
                                    if theta==(l+6)
                                        A(l+j,theta+2+k)=1;
                                    end
                                end
                            end
                            k=k+1;
                        end
                    end
                end
            end
    
    
    
    
    
    
        
    persistent waypoints0 traj_time d0
    if nargin > 2
        d = waypoints(:,2:end) - waypoints(:,1:end-1);
        d0 = 2 * sqrt(d(1,:).^2 + d(2,:).^2 + d(3,:).^2);
        traj_time = [0, cumsum(d0)];
        waypoints0 = waypoints;
        
        
    else
        if t >= traj_time(end)
            t = traj_time(end);
        end
        t_index = find(traj_time > t,1) - 1;
        
        if (t_index == 0)
            t_index = 1;
        end
        if(t == 0)
            desired_state.pos = waypoints0(:,1);
        else
            scale = (t-traj_time(t_index)) / d0(t_index);
            index = [(t_index-1)*8+1:t_index*8];
            
            nn=size(waypoints0(1,:))
            n=nn(2)
            Coeffmat_x,Value_x = pols_coef_retrn(n,waypoints0(1,:)');
            Coeffmat_y,Value_y = pols_coef_retrn(n,waypoints0(2,:)');
            Coeffmat_z,Value_z = pols_coef_retrn(n,waypoints0(3,:)');
            coeff_x=Value_x/Coeffmat_x;
            coeff_y=Value_y/Coeffmat_y;
            coeff_z=Value_z/Coeffmat_z;
            
            desired_state.pos = [coeff_x(index)'*t_mat1(scale);coeff_y(index)'*t_mat1(scale);coeff_z(index)'*t_mat1(scale);]
            desired_state.vel = [coeff_x(index)'*t_mat2(scale);coeff_y(index)'*t_mat2(scale);coeff_z(index)'*t_mat2(scale);]
            desired_state.acc = [coeff_x(index)'*t_mat3(scale);coeff_y(index)'*t_mat3(scale);coeff_z(index)'*t_mat3(scale);]
        end
        
        desired_state.yaw = 0;
        desired_state.yawdot = 0;
    end
end

Here is the error message

Array indices must be positive integers or logical values.

Error in traj_generator (line 110)
        if t >= traj_time(end)

Error in runsim (line 20)
 trajhandle(waypoints); 

Answer 1

[Guillaume]

You should read the comments at the top of the function and understand them.

In particular, the function must be initialised first by calling it with

trajectory_generator([], [], waypoints);

where waypoints is a 3xN matrix.

Only then can you use it with

desired_state = traj_generator(t, state);

The error you see occurs when traj_time is empty (end is indeed an invalid index in that case). And traj_time can only be empty if the function has not been initialised.

Granted, the function should check that it's been initialised before using the persistent variables. You should add than check.

...and take out the nested functions which should be local functions

...and indent the code properly to make it easier to read and debug

...and fix all the missing semicolons and any other mlint warning