The function subs(e) is equivalent to eval(e).

The function subs(e,n) replaces occurences of the default variable in e with the expression n.  The default variable is determined by findsym(e,1).

For scalar o, the function subs(e,o,n) replaces occurences of o, in the expression e, with n. If n is a vector or matrix, then the operations ^, + and * (and therefore - and /) are performed element-wise.

For non-scalar o, the function subs(e,o,n), replaces each element of o with the corresponding element of n. In this case, the structure and size of o and n must be the same.  The substitution of elements occurs in series.

$\mathrm{with}\left(\mathrm{MTM}\right)\:$

$\mathrm{subs}\left(x+y\,3\right)$

$3+y$

$\mathrm{subs}\left(x+y\,y\,3\right)$

$x+3$

$\mathrm{subs}\left(xy\,y\,\mathrm{Array}\left(\left[\left[1\,2\right]\,\left[3\,4\right]\right]\right)\right)$

$\left[\begin{array}{cc}x& 2x\\ 3x& 4x\end{array}\right]$

$\mathrm{subs}\left(xy\,\left[x\,y\right]\,\left[\mathrm{Array}\left(\left[\left[1\,2\right]\,\left[3\,4\right]\right]\right)\,\mathrm{Array}\left(\left[\left[1\,2\right]\,\left[3\,5\right]\right]\right)\right]\right)$

$\left[\begin{array}{cc}1& 4\\ 9& 20\end{array}\right]$

$\mathrm{subs}\left(x+y+z\,\left[x\,y\right]\,\left[y\,z\right]\right)$

$3z$

$\mathrm{subs}\left(x+y+z\,\left[x\,y\right]\,\left[z\,x\right]\right)$

$2z+x$