Info Catalog calc: Operations on Variables calc: Store and Recall calc: Evaluates-To Operator

calc: Let Command

 
 13.4 The Let Command
 ====================
 
 If you have an expression like ‘a+b^2’ on the stack and you wish to
 compute its value where ‘b=3’, you can simply store 3 in ‘b’ and then
 press ‘=’ to reevaluate the formula.  This has the side-effect of
 leaving the stored value of 3 in ‘b’ for future operations.
 
    The ‘s l’ (‘calc-let’) command evaluates a formula under a
 _temporary_ assignment of a variable.  It stores the value on the top of
 the stack into the specified variable, then evaluates the second-to-top
 stack entry, then restores the original value (or lack of one) in the
 variable.  Thus after ‘' a+b^2 <RET> 3 s l b <RET>’, the stack will
 contain the formula ‘a + 9’.  The subsequent command ‘5 s l a <RET>’
 will replace this formula with the number 14.  The variables ‘a’ and ‘b’
 are not permanently affected in any way by these commands.
 
    The value on the top of the stack may be an equation or assignment,
 or a vector of equations or assignments, in which case the default will
 be analogous to the case of ‘s t <RET>’.  Storing Variables.
 
    Also, you can answer the variable-name prompt with an equation or
 assignment: ‘s l b=3 <RET>’ is the same as storing 3 on the stack and
 typing ‘s l b <RET>’.
 
    The ‘a b’ (‘calc-substitute’) command is another way to substitute a
 variable with a value in a formula.  It does an actual substitution
 rather than temporarily assigning the variable and evaluating.  For
 example, letting ‘n=2’ in ‘f(n pi)’ with ‘a b’ will produce ‘f(2 pi)’,
 whereas ‘s l’ would give ‘f(6.28)’ since the evaluation step will also
 evaluate ‘pi’.
 

Info Catalog calc: Operations on Variables calc: Store and Recall calc: Evaluates-To Operator