Why am I getting index must be positive integer or local error?

for ind=0:1920
    U=3*ind+linspace(1,3,3);
    k= PHI_disp_RBME_ModePlot_N(ind);
    r=xlocs_full(ind);
end
i=sqrt(-1);
displ=U*exp(i*(k*r));
disp(displ);

Error is for line 6(k=PHI...)

Answer 1

[Image Analyst]

It's all described very well in the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_fix_the_error_.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22.3F