1 files changed, 72 insertions, 0 deletions
diff --git a/noao/digiphot/daophot/daolib/invers2.x b/noao/digiphot/daophot/daolib/invers2.x
new file mode 100644
index 00000000..5393c6ea
--- /dev/null
+++ b/noao/digiphot/daophot/daolib/invers2.x
@@ -0,0 +1,72 @@
+define	TINY	(1.0e-15)
+
+# INVERS
+#
+# Although it seems counter-intuitive, the tests that I have run
+# so far suggest that the 180 x 180 matrices that NSTAR needs can
+# be inverted with sufficient accuracy if the elements are REAL*4
+# rather than REAL*8.
+#
+# Arguments
+# 
+#     a (input/output) is a square matrix of dimension N.  The inverse 
+#       of the input matrix A is returned in A.
+#
+#   nmax (input) is the size assigned to the matrix A in the calling 
+#       routine.  It is needed for the dimension statement below.
+#
+# iflag (output) is an error flag.  iflag  =  1 if the matrix could not
+#       be inverted; iflag  =  0 if it could.
+#
+# This is an SPP translation of the original fortran version with the
+# addition of a check for tiny numbers which could cause an FPE.
+
+procedure invers2 (a, nmax, n, iflag)
+
+real	a[nmax,nmax]
+int	nmax
+int	n
+int	iflag
+
+int	i, j, k
+
+begin
+      # Check for tiny numbers.
+      do i = 1, n
+        do j = 1, n
+	  if (abs (a[i,j]) < TINY)
+	      a[i,j] = 0e0
+
+      # Original code.
+      iflag = 0
+      i = 1
+   30 if (a[i,i] .eq. 0.0e0) goto 91
+      a[i,i] = 1.0e0 / a[i,i]
+      j = 1
+   31 if (j .eq. i) goto  34
+      a[j,i] = -a[j,i] * a[i,i]
+      k = 1
+   32 if (k .eq. i) goto  33
+      a[j,k] = a[j,k] + a[j,i] * a[i,k]
+   33 if (k .eq. n) goto  34
+      k = k + 1
+      goto  32
+   34 if (j .eq. n) goto  35
+      j = j + 1
+      goto  31
+   35 k = 1
+   36 if (k .eq. i) goto  37
+      a[i,k] = a[i,k] * a[i,i]
+   37 if (k .eq. n) goto  38
+      k = k + 1
+      goto  36
+   38 if (i .eq. n) return
+      i = i+1
+      goto  30
+
+# Error:  zero on the diagonal.
+
+ 91 iflag = 1
+      return
+
+end