CODEWITHSUNDEEP
pythonpython-2.7fortrannumbers
i'mlaguiar
i'mlaguiar

Reputation: 21

Same equation on both Fortran 95 and Python return different results

There is a equation in Fortran 95 to calculate some position for an array, I copied and pasted the same equation in Python, but they return different results.

EDIT: on the rush for an answer, I forgot to show the declarations of the variables, but they are in the Fortran code example now. And it turns out the declaration was the problem, thanks to @SurestTexas and @albert for pointing it out in the comments, and everyone else who helped.

The equation in Fortran: 

integer(2) :: i, j
integer(4) :: e, n_x
n_x = 1162
j = ((-2.8 - (-8.4)) / 0.05) + 1
i = ((-4.5 - (-5.1)) / 0.05) + 1 
e = ((i-1)*n_x+j)

I print e, which results in: 12894

And in Python:

n_x = 1162
j = ((-2.8 - (-8.4)) / 0.05) + 1
i = ((-4.5 - (-5.1)) / 0.05) + 1 
e = ((i-1)*n_x+j)

I print e, which results in: 14057.0

As you can see, they are exactly the same, I can't find out what is wrong and how I can solve the issue, please help me.

Upvotes: 0

Views: 273

Answers (2)

marya
marya

Reputation: 94

supplement：

Interesting that in Python 3.5.3, e is printed as 14056.99999999999.

The implicit none statement is used to inhibit a very old feature of Fortran that by default treats all variables that start with the letters i, j, k, l, m and n as integers and all other variables as real arguments.

I can't comment due to insufficient reputation, so put it in Answer as a record of my research.

Upvotes: 2

Paula Thomas
Paula Thomas

Reputation: 1190

Remembering my FORTRAN. I think it assumes datatype based on the first letter of the variable, in partilar i and j would be integers So to simulate this in Python I did:

n_x = 1162
j = int(((-2.8 - (-8.4)) / 0.05) + 1)
i = int(((-4.5 - (-5.1)) / 0.05) + 1 )
e = ((i-1)*n_x+j)

Which gave me 12895

Upvotes: 2

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