matlab中总出现Undefined function 'conv' for input arguments of type 'double'.求解释

% 用 edit conv.m 看看有没有或者坏没坏 function c = conv(a, b)%CONV Convolution and polynomial multiplication.% C = CONV(A, B) convolves vectors A and B. The resulting% vector is length LENGTH(A)+LENGTH(B)-1.% If A and B are vectors of polynomial coefficients,