root / synthbench / euroben-dm / mod2ci / .svn / text-base / givens.f.svn-base @ 0:839f52ef7657
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Subroutine givens( a, b, c, s ) |
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! ---------------------------------------------------------------------- |
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! --- Calculates rotation factors c & s from 'a' and 'b' for the Givens |
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! transformation (used in rgmres). |
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! ---------------------------------------------------------------------- |
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Use numerics |
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Use floptime |
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Implicit None |
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|
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Real(l_) :: a, b, c, s |
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|
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Real(l_) :: fac |
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! ---------------------------------------------------------------------- |
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If ( b == 0.0_l_ ) Then |
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c = 1.0_l_ |
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s = 0.0_l_ |
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Else If ( Abs( b ) < Abs( a ) ) Then |
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fac = -a/b |
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s = 1.0_l_/Sqrt( 1.0_l_ + fac*fac ) |
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c = fac*s |
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flops = flops + 13 |
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Else |
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fac = -b/a |
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c = 1.0_l_/Sqrt( 1.0_l_ + fac*fac ) |
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s = fac*c |
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flops = flops + 13 |
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End If |
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! ---------------------------------------------------------------------- |
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End Subroutine givens |