If..then..elseif...then.. Endif ???

[vinu]

Hi members,

I have a question.

Is there any computational speed difference
between using two 'IF' statements seperately
and using one 'IF ELSEIF' statement together?

eg:

Type-1
if (a .eq. b) then
(do something)
endif
if (a .eq. c) then
(do something)
endif

Type-2
if (a .eq. b) then
(do something)
elseif (a .eq. c) then
(do something)
endif


Are these type-1 and type-2 equally fast ?


Please say an answer if you know,
-Vinu

[rocksea]

Both the functions are not same (i.e. you may not get same results!)

If a=b=c (a possible case):

In type 1, both steps are processed
In type 2, only the first step is processed.

If we consider such a possibility, checking the speed is logically incorrect.

---------------------------------------------------------------------

Then, still if we want to check the speed, there is a possibility that type 2 is faster.
Let me explain how:

In most of the softwares, the value/expression for a variable is estimated only when it is called.
(For example you must be knowing that in Ferret, an expression is processed only if the
variable is called).
Suppose your a, b & c are results of some mathematical expressions/formulas.

In type 1, values of a, b & c are calculated in all cases as all the 3 variables are checked for equivalence.
In type 2, value of c may not be calculated in several cases.
Hence in type 1 you end up with more calculations making it slower than type 1.

[vinu]

Good logic.

I do agree the type-1 and type-2 are different.

type-1 is safe but consumes time and awkard,
if your argument on speed is correct.

There are many places "if" statement occurs
in our code and I was thinking to replace it with
"if elseif then", for cost effect computation.

But now i think, it should be done with caution.

Thanks for your help

-Vinu

[praveen]

vinu,roxy

yea. u are right. This one is a problem for the present models. Most of the model codes are not well structured for faster performance.

best wishes for your effort. :thumbsup:

[rabin_xu]

I think the first is faster than the second