28 lines
702 B
Fortran
28 lines
702 B
Fortran
subroutine drotgf(da,db,c,s)
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c
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c construct givens plane rotation.
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c jack dongarra, linpack, 3/11/78.
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c
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double precision da,db,c,s,roe,scale,r,z
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c
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roe = db
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if( dabs(da) .gt. dabs(db) ) roe = da
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scale = dabs(da) + dabs(db)
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if( scale .ne. 0.0d0 ) go to 10
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c = 1.0d0
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s = 0.0d0
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r = 0.0d0
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z = 0.0d0
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go to 20
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10 r = scale*dsqrt((da/scale)**2 + (db/scale)**2)
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r = dsign(1.0d0,roe)*r
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c = da/r
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s = db/r
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z = 1.0d0
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if( dabs(da) .gt. dabs(db) ) z = s
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if( dabs(db) .ge. dabs(da) .and. c .ne. 0.0d0 ) z = 1.0d0/c
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20 da = r
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db = z
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return
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end
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