## MA02FD

### Hyperbolic plane rotation

[Specification] [Arguments] [Method] [References] [Comments] [Example]

Purpose

      To compute the coefficients c and s (c^2 + s^2 = 1) for a modified
      hyperbolic plane rotation, such that,

          y1 := 1/c * x1 - s/c * x2 = sqrt(x1^2 - x2^2),
          y2 :=  -s * y1 +  c  * x2 = 0,

      given two real numbers x1 and x2, satisfying either x1 = x2 = 0,
      or abs(x2) < abs(x1).

Specification

          SUBROUTINE MA02FD( X1, X2, C, S, INFO )
    C     .. Scalar Arguments ..
          DOUBLE PRECISION  X1, X2, C, S
          INTEGER           INFO

Arguments

Input/Output Parameters

      X1      (input/output) DOUBLE PRECISION
              On entry, the real number x1.
              On exit, the real number y1.

      X2      (input) DOUBLE PRECISION
              The real number x2.
              The values x1 and x2 should satisfy either x1 = x2 = 0, or
              abs(x2) < abs(x1).

      C       (output) DOUBLE PRECISION
              The cosines c of the modified hyperbolic plane rotation.

      S       (output) DOUBLE PRECISION
              The sines s of the modified hyperbolic plane rotation.

Error Indicator

      INFO    INTEGER
              = 0:  succesful exit;
              = 1:  if abs(x2) >= abs(x1) and either x1 <> 0 or x2 <> 0.

Further Comments

      None

Example

Program Text

      None

Program Data

      None

Program Results

      None

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