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Several mechanisms are available for saving and retrieving previously evaluated
expressions. The simplest of these refers to the last algebraic expression simplified.
When an assignment of an algebraic expression is made, or an expression is evaluated at
the top level, (i.e., not inside a compound statement or procedure) the results of the
evaluation are automatically saved in a variable ws
that we shall refer to as the
workspace. (More precisely, the expression is assigned to the variable ws
that is then
available for further manipulation.)
Example:
If we evaluate the expression (x+y)^2
at the top level and next wish to differentiate it
with respect to y
, we can simply say
df(ws,y);
to get the desired answer.
If the user wishes to assign the workspace to a variable or expression for later use, the
saveas
statement can be used. It has the syntax
saveas
\(\langle \)expression\(\rangle \)For example, after the differentiation in the last example, the workspace holds the
expression 2*x+2*y
. If we wish to assign this to the variable z
we can now
say
saveas z;
If the user wishes to save the expression in a form that allows him to use some of its
variables as arbitrary parameters, the for all
command can be used.
Example:
for all x saveas h(x);
with the above expression would mean that h(z)
evaluates to 2*y+2*z
.
A further method for referencing more than the last expression is described in chapter 13 on interactive use of REDUCE.
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