How to debug this code?

Makefile

FC = ifort
FCFLAGS= -O0 -debug -traceback -check -ftrapuv

TARGETS= clean birrp

OBJSOC= strlen.f diagnostic.f math.f rtpss.f zlinpack.f coherence.f fft.f rarfilt.f utils.f dataft.f filter.f response.f weight.f  birrp.f
all:  $(TARGETS)    

clean:$
        rm -f *.o *.mod
        rm -f birrp
        
birrp:$(OBJSOC)
        $(FC) $(FCFLAGS) -o $@ $(OBJSOC)

# General compile rules

.SUFFIXES: .f .o

.f .o:    
    $(FC) $(FCFLAGS) -c -o $@ $<

I compile the code

./birrp < n128.in
 select the input level (0=basic,1=advanced): input the number of output time series: input the number of input time series: select tbw for prolate data window (1 to 4): input the data sample interval: input the initial section length and maximum number of sections:  table of output periods by section length
   125.0000       83.33334    
   62.50000       41.66667    
   31.25000       20.83333    
   15.62500       10.41667    
   7.812500       5.208333    
   3.906250       2.604167    
   1.953125       1.302083    
  0.9765625      0.6510417    
 are these values acceptable (y or n)? input the robustness and leverage parameters (0 and >0.99 are recommended): input the 2nd stage coherence threshold: input the output filename root: input the output level (-3 to 3): input the number of data pieces: input the length of the ar filter (0 for none, <0 for filename): select the file mode (0=separate ascii files, 1=separate binary files 2=all component ascii files 3=ts ascii file: select the input mode (0=by points, 1=by date/time): input the number of points to read: input the number of filter parameters (<0 for filename): input the data filename: input the number of points to skip: input the number of filter parameters (<0 for filename): input the data filename: input the number of points to skip: input the number of filter parameters (<0 for filename): input the filter filename: input the data filename: input the number of points to skip: input the number of filter parameters (<0 for filename): input the filter filename: input the data filename: input the number of points to skip: input the number of filter parameters (<0 for filename): input the filter filename: input the data filename: input the number of points to skip: input the number of filter parameters (<0 for filename): input the filter filename: input the data filename: input the number of points to skip:forrtl: error (182): floating invalid - possible uninitialized real/complex variable.
Image              PC                Routine            Line        Source             
birrp              0000000000656D55  Unknown               Unknown  Unknown
birrp              0000000000654977  Unknown               Unknown  Unknown
birrp              00000000006077D4  Unknown               Unknown  Unknown
birrp              00000000006075E6  Unknown               Unknown  Unknown
birrp              00000000005BF7F6  Unknown               Unknown  Unknown
birrp              00000000005C30B7  Unknown               Unknown  Unknown
libpthread.so.0    00007FD7D61433D0  Unknown               Unknown  Unknown
birrp              0000000000431396  xmedian_                 2078  math.f
birrp              000000000056B85A  MAIN__                    782  birrp.f
birrp              000000000040292E  Unknown               Unknown  Unknown
libc.so.6          00007FD7D5B85830  Unknown               Unknown  Unknown
birrp              0000000000402829  Unknown               Unknown  Unknown
Aborted (core dumped)

I am attaching the folder.Downloadb.tar.gz