An array for multiple LHS assignment cannot contain LEX_TS_STRING error - matlab

Question

New to programing in matlab. I am currently trying to make a MATLAB program that will find the critical values of a multi-variable function and tell me whether each are a minimum, maximum, or saddle point. Unfortunately I always get the error : An array for multiple LHS assignment cannot contain LEX_TS_STRING
Any help will be very appreciated.
here's the code:
function [c,d] = critcalpoints(f)
syms x y
f(x,y)=x^3-3*x^2+5*x*y-7*y^2;
gradf = jacobian(f(x,y));
hessmatf = jacobian(gradf,[x,y]);
[xcr,ycr]=solve(gradf(1),gradf(2));
H1=subs(hessmatf,[x,y],[xcr(1),ycr(1)]);
H2=subs(hessmatf,[x,y],[xcr(2),ycr(2)]);
eig(H1);
eig(H2);
c = double(eig(H1));
d = double(eig(H2));
if (c(1) > 0 && d(1) > 0) || (c(2) > 0 && d(2) > 0)
print([xcr,ycr],' is a minimum')
elseif (c(1) < 0 && d(1) < 0) || (c(2) < 0 && d(2) < 0)
print( [xcr, ycr], ' is a maximum')
elseif (c(1) < 0 && d(1) > 0) || (c(1) > 0 && d(1) < 0)
print( [xcr, ycr], ' is a saddle point')
elseif (c(2) < 0 && d(2) > 0) || (c(2) > 0 && d(2) < 0)
print( [xcr, ycr], ' is a saddle point')
elseif (c(1)==0 || d(1)==0)
print( [xcr, ycr], ' is degenerate')
elseif (c(2)==0 || d(2)==0)
print( [xcr, ycr], ' is degenerate')
end

Answer 1

Cannot reproduce your error. The code can work but you need to change print to something else as print doesn't do what you think it does. The print function prints a figure that is open to file. Change it so that you display xcr and ycr first then display the right condition to satisfy after. Use disp instead:
syms x y
f(x,y)=x^3-3*x^2+5*x*y-7*y^2;
gradf = jacobian(f(x,y));
hessmatf = jacobian(gradf,[x,y]);
[xcr,ycr]=solve(gradf(1),gradf(2));
H1=subs(hessmatf,[x,y],[xcr(1),ycr(1)]);
H2=subs(hessmatf,[x,y],[xcr(2),ycr(2)]);
eig(H1);
eig(H2);
c = double(eig(H1));
d = double(eig(H2));
disp([xcr, ycr]); % Display the solutions first
if (c(1) > 0 && d(1) > 0) || (c(2) > 0 && d(2) > 0)
disp('is a minimum')
elseif (c(1) < 0 && d(1) < 0) || (c(2) < 0 && d(2) < 0)
disp('is a maximum')
elseif (c(1) < 0 && d(1) > 0) || (c(1) > 0 && d(1) < 0)
disp('is a saddle point')
elseif (c(2) < 0 && d(2) > 0) || (c(2) > 0 && d(2) < 0)
disp('is a saddle point')
elseif (c(1)==0 || d(1)==0)
disp('is degenerate')
elseif (c(2)==0 || d(2)==0)
disp('is degenerate')
end
I get:
[ 0, 0]
[ 59/42, 295/588]
is a maximum