if condition for infinity

Question

SITI AISHAH 2019-4-19

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/457373-if-condition-for-infinity

评论： madhan ravi 2019-4-20

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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Answer 1

John D'Errico 2019-4-19

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https://ww2.mathworks.cn/matlabcentral/answers/457373-if-condition-for-infinity#answer_371353

编辑：John D'Errico 2019-4-19

在 MATLAB Online 中打开

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.

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SITI AISHAH 2019-4-20

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 ?