"Index in position 1 exceeds array bounds (must not exceed 1)." error using spline.

function [E,B,cmd,vx,vy] = trajplanner(a,x,N,T)

% trajplanner function creates a path and calculates the velocity of the
% end effector along path at various times
%   inputs:
%       a = column vector containing sections' lengths a1 & a2
%       x = 2-by-N matrix containing target positions of end-effector;
%           each column is one point (xi,yi)
%       N = integer that equals # of intermediate configurations
%           needing interpolation
%       T = total duration of the trip from first to last point
%   outputs:
%       E = 2-by-N matrix containing path end-effector will follow
%       B = 2-by-N matrix containing path joint B will follow
%       cmd = 2-by-N matrix containing joint angle commands
%       vx = array of length N containing x-component of velocity
%       vy = array of length N containing y-component of velocity

eP=length(x);                           % # of effector points
xq=linspace(x(1,1),x(1,eP),N);

E=[xq;zeros(1,N)];                      % create matrix for E
E(2,:)=spline(x(1,:),x(2,:),xq);
B=zeros(2,eP);                          % create matrix for B
cmd=zeros(2,eP);

                                        % For loop to move through xqyq
for ii=1:N
    cmd(:,ii)=ikFS(a,E(:,ii),[1;1]);
    B(:,ii)=[a(1,1)*cos(cmd(1,ii));a(1,1)*sin(cmd(1,ii))];
end

                                        % snapshots at intermediate positions
plot([zeros(1,N);B(1,:);E(1,:)],[zeros(1,N);B(2,:);E(2,:)],'k')
hold on
axis equal

plot(E(1,:),E(2,:),'g','linewidth',2)   % trajectory at intermediate positions

pt_size = 1000;                         % mark user-defined points
scatter(x(1,:),x(2,:),pt_size,'.')

xpos=E(1,1:N);
ypos=E(2,1:N);
vx = (gradient(xpos)/steps)'
vy = (gradient(ypos)/steps)'

xE = cumtrapz(linspace(0,T,N),vx)+x(1,2);
yE = cumtrapz(linspace(0,T,N),vy)+x(1,2);
plot(xE,yE)

end

Running the program with a = [2,1], N = 50, T = 1, and x = [a(1) a(1)/2 0 -a(1) -a(1)-a(2) 0 a(1)/2 a(1) a(1) 0] returns:

"Index in position 1 exceeds array bounds (must not exceed 1).

Error in trajplanner (line 23)

E(2,:)=spline(x(1,:),x(2,:),xq);"

Any suggestions on how to fix this?

Answer 1

[Cris LaPierre]

I suspect the issue is your indexing of your variable x is the issue. I don't think it has a 2nd row, so your call to x(2,:) results in an error.

a = [2,1];
x = [a(1) a(1)/2 0 -a(1) -a(1)-a(2) 0 a(1)/2 a(1) a(1) 0]

x = 1×10

2 1 0 -2 -3 0 1 2 2 0

●

x(2,:)

Index in position 1 exceeds array bounds (must not exceed 1).