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| author | Siddhesh Wani | 2015-05-25 14:46:31 +0530 |
|---|---|---|
| committer | Siddhesh Wani | 2015-05-25 14:46:31 +0530 |
| commit | db464f35f5a10b58d9ed1085e0b462689adee583 (patch) | |
| tree | de5cdbc71a54765d9fec33414630ae2c8904c9b8 /src/fortran/blas/drotg.f | |
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Original Version
Diffstat (limited to 'src/fortran/blas/drotg.f')
| -rw-r--r-- | src/fortran/blas/drotg.f | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/src/fortran/blas/drotg.f b/src/fortran/blas/drotg.f new file mode 100644 index 0000000..67838e2 --- /dev/null +++ b/src/fortran/blas/drotg.f @@ -0,0 +1,27 @@ + subroutine drotg(da,db,c,s) +c +c construct givens plane rotation. +c jack dongarra, linpack, 3/11/78. +c + double precision da,db,c,s,roe,scale,r,z +c + roe = db + if( dabs(da) .gt. dabs(db) ) roe = da + scale = dabs(da) + dabs(db) + if( scale .ne. 0.0d0 ) go to 10 + c = 1.0d0 + s = 0.0d0 + r = 0.0d0 + z = 0.0d0 + go to 20 + 10 r = scale*dsqrt((da/scale)**2 + (db/scale)**2) + r = dsign(1.0d0,roe)*r + c = da/r + s = db/r + z = 1.0d0 + if( dabs(da) .gt. dabs(db) ) z = s + if( dabs(db) .ge. dabs(da) .and. c .ne. 0.0d0 ) z = 1.0d0/c + 20 da = r + db = z + return + end |