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if condition for infinity

Asked by SITI AISHAH on 19 Apr 2019
Latest activity Commented on by madhan ravi
on 20 Apr 2019
Please help me regarding this;
slenderness = input ('what is your l/d?')
if slenderness == 1
Sommerfeld = input ('Please enter your Sommerfeld Number')
interp1 (Somm_Num,Flow_Variable_1,Sommerfeld)
elseif slenderness == 1/2
Sommerfeld = input ('Please enter your Sommerfeld Number')
interp1 (Somm_Num,Flow_Variable_2,Sommerfeld)
elseif slenderness == 1/4
Sommerfeld = input ('Please enter your Sommerfeld Number')
interp1 (Somm_Num,Flow_Variable_3,Sommerfeld)
elseif slenderness == infinity
Sommerfeld = input ('Please enter your Sommerfeld Number')
interp1 (Somm_Num,Flow_Variable_4,Sommerfeld)
end
my slenderness is infinity, but when i enter that,it says 'error using input'

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1 Answer

John D'Errico
Answer by John D'Errico
on 19 Apr 2019
Edited by John D'Errico
on 19 Apr 2019

You cannot test for the word 'finite', and expect it to return a valid result, when compared to an inf value.
x = inf
x =
Inf
>> x == 'finite'
ans =
1×6 logical array
0 0 0 0 0 0
>> x == inf
ans =
logical
1
>> isinf(x)
ans =
logical
1
However, you can use the function isinf, which will return true for either -inf or +inf.
Personally, I would STRONGLY suggest that you learn to use and write functions, instead of relying on tools like input in the first place.

  2 Comments

SITI AISHAH on 20 Apr 2019
I have test for infinity before, then I try the word'finite' since it says error using input. Instead of the word infinity, what should I write to represent for infinity value ?
madhan ravi
on 20 Apr 2019
SITI AISHAH answer moved here:
It's simple! I have tried replace the word 'infinity' with Inf, and the script is running without any error. yeszza!!!

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