gcc - gfortran compiler Error: result of exponentiation exceeds the range of INTEGER(4)

Question

I have this line in fortran and I'm getting the compiler error in the title. dFeV is a 1d array of reals.
dFeV(x)=R1*5**(15) * (a**2) * EXP(-(VmigFe)/kbt)
for the record, the variable names are inherited and not my fault. I think this is an issue with not having the memory space to compute the value on the right before I store it on the left as a real (which would have enough room), but I don't know how to allocate more space for that computation.

Answer 1

The problem arises as one part of your computation is done using integer arithmetic of type integer(4). That type has an upper limit of 2^31-1 = 2147483647 whereas your intermediate result 5^15 = 30517578125 is slightly larger (thanks to @evets comment).

As pointed out in your question: you save the result in a real variable. Therefor, you could just compute that exponentiation using real data types: 5.0**15. Your formula will end up like the following

dFeV(x)= R1 * (5.0**15) * (a**2) * exp(-(VmigFe)/kbt)

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Note that integer(4) need not be the same implementation for every processor (thanks @IanBush). Which just means that for some specific machines the upper limit might be different from 2^31-1 = 2147483647.