What is mean by "undefined reference"?

[szepink]

Hi guys,

I'm a beginner in Fortran. i was trying to compile a program but errors below appeared:

/tmp/ifortMMF3EI.o: In function `MAIN__':
file5.f.text+0x404): undefined reference to `ddriv2_'
file5.f.text+0x702): undefined reference to `rffti_'
file5.f.text+0x712): undefined reference to `rfftf_'

what does this mean? I am using Fortran 95. the program comes with subprograms. Thanks.

 

[mikrom]

Probably the functions rfftf, rffti, ddriv2 which should be used in your program are absent.