Fancy Matlab

>> help subs

 SUBS   Symbolic substitution.
    SUBS(S) replaces all the variables in the symbolic expression S with
    values obtained from the calling function, or the MATLAB workspace.

    SUBS(S,NEW) replaces the free symbolic variable in S with NEW.
    SUBS(S,OLD,NEW) replaces OLD with NEW in the symbolic expression S.
    OLD is a symbolic variable, a string representing a variable name, or
    a string (quoted) expression. NEW is a symbolic or numeric variable
    or expression.

    If OLD and NEW are cell arrays of the same size, each element of OLD is
    replaced by the corresponding element of NEW.  If S and OLD are scalars
    and NEW is an array or cell array, the scalars are expanded to produce
    an array result.  If NEW is a cell array of numeric matrices, the
    substitutions are performed elementwise (i.e., subs(x*y,{x,y},{A,B})
    returns A.*B when A and B are numeric).

    If SUBS(S,OLD,NEW) does not change S, then SUBS(S,NEW,OLD) is tried.
    This provides backwards compatibility with previous versions and
    eliminates the need to remember the order of the arguments.
    SUBS(S,OLD,NEW,0) does not switch the arguments if S does not change.

    Examples:
      Single input:
        Suppose a = 980 and C1 = 3 exist in the workspace.
        The statement
           y = dsolve('Dy = -a*y')
        produces
           y = exp(-a*t)*C1
        Then the statement
           subs(y)
        produces
           ans = 3*exp(-980*t)

      Single Substitution:
        subs(a+b,a,4) returns 4+b.

      Multiple Substitutions:
        subs(cos(a)+sin(b),{a,b},{sym('alpha'),2}) returns
        cos(alpha)+sin(2)

      Scalar Expansion Case:
        subs(exp(a*t),'a',-magic(2)) returns

        [   exp(-t), exp(-3*t)]
        [ exp(-4*t), exp(-2*t)]

      Multiple Scalar Expansion:
        subs(x*y,{x,y},{[0 1;-1 0],[1 -1;-2 1]}) returns
        [  0, -1]
        [  2,  0]

    See also SUBEXPR

 Overloaded methods
    help sym/subs.m

# posted by samuel @ 8:00 AM