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# Calling a function only when needed

## Calling a function only when needed

(OP)
Hi,

In a Mathcad program, I noticed that a function is recalculated while it does not need to be. Here is an example:

f(x):= x^2 + 1

g(x,y):= f(x) + y

y:= 0,1 .. 10

[graph of g(x,y) vs. y]

Normally, when y is varied, f(x) should not be recalculated, it should be calculated only for the first value of y. But I noticed that f(x) is calculated for each value of y.

Is there a way to force the program to calculate f(x) only once for all?

Thanks a lot,

JC

### RE: Calling a function only when needed

No, your g(x,y) call is a new call for each value of y, so f(x) is also called.  If it's that annoying then you should just precompute f(x) and substitute the resultant into g(x,y).

### RE: Calling a function only when needed

Would you do that by

i=0,1;10
g(f(x),i)=fx+y

?

### RE: Calling a function only when needed

if fx is such that fx=f(x), then yes.

### RE: Calling a function only when needed

I recently did a calculation and this function recalculation proved to be quite a bit of problem (calculations took e.g. 10-15mins, whereas the same calculation done as a Flash program was executed in a minute or two). The way I used to get around this problem was switching to using matrices instead of functions. The speed of calculations was greatly improved...

(Your example would be f[x:=x^2+1 and g[x,y:=f[x +y)

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