numeric-linalg
Educational material on the SciPy implementation of numerical linear algebra algorithms
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| lapack/TESTING/EIG/ssxt1.f | 3978B | -rw-r--r-- |
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*> \brief \b SSXT1 * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * * Definition: * =========== * * REAL FUNCTION SSXT1( IJOB, D1, N1, D2, N2, ABSTOL, * ULP, UNFL ) * * .. Scalar Arguments .. * INTEGER IJOB, N1, N2 * REAL ABSTOL, ULP, UNFL * .. * .. Array Arguments .. * REAL D1( * ), D2( * ) * .. * * *> \par Purpose: * ============= *> *> \verbatim *> *> SSXT1 computes the difference between a set of eigenvalues. *> The result is returned as the function value. *> *> IJOB = 1: Computes max { min | D1(i)-D2(j) | } *> i j *> *> IJOB = 2: Computes max { min | D1(i)-D2(j) | / *> i j *> ( ABSTOL + |D1(i)|*ULP ) } *> \endverbatim * * Arguments: * ========== * *> \param[in] IJOB *> \verbatim *> IJOB is INTEGER *> Specifies the type of tests to be performed. (See above.) *> \endverbatim *> *> \param[in] D1 *> \verbatim *> D1 is REAL array, dimension (N1) *> The first array. D1 should be in increasing order, i.e., *> D1(j) <= D1(j+1). *> \endverbatim *> *> \param[in] N1 *> \verbatim *> N1 is INTEGER *> The length of D1. *> \endverbatim *> *> \param[in] D2 *> \verbatim *> D2 is REAL array, dimension (N2) *> The second array. D2 should be in increasing order, i.e., *> D2(j) <= D2(j+1). *> \endverbatim *> *> \param[in] N2 *> \verbatim *> N2 is INTEGER *> The length of D2. *> \endverbatim *> *> \param[in] ABSTOL *> \verbatim *> ABSTOL is REAL *> The absolute tolerance, used as a measure of the error. *> \endverbatim *> *> \param[in] ULP *> \verbatim *> ULP is REAL *> Machine precision. *> \endverbatim *> *> \param[in] UNFL *> \verbatim *> UNFL is REAL *> The smallest positive number whose reciprocal does not *> overflow. *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \ingroup single_eig * * ===================================================================== REAL FUNCTION SSXT1( IJOB, D1, N1, D2, N2, ABSTOL, $ ULP, UNFL ) * * -- LAPACK test routine -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * * .. Scalar Arguments .. INTEGER IJOB, N1, N2 REAL ABSTOL, ULP, UNFL * .. * .. Array Arguments .. REAL D1( * ), D2( * ) * .. * * ===================================================================== * * .. Parameters .. REAL ZERO PARAMETER ( ZERO = 0.0E0 ) * .. * .. Local Scalars .. INTEGER I, J REAL TEMP1, TEMP2 * .. * .. Intrinsic Functions .. INTRINSIC ABS, MAX, MIN * .. * .. Executable Statements .. * TEMP1 = ZERO * J = 1 DO 20 I = 1, N1 10 CONTINUE IF( D2( J ).LT.D1( I ) .AND. J.LT.N2 ) THEN J = J + 1 GO TO 10 END IF IF( J.EQ.1 ) THEN TEMP2 = ABS( D2( J )-D1( I ) ) IF( IJOB.EQ.2 ) $ TEMP2 = TEMP2 / MAX( UNFL, ABSTOL+ULP*ABS( D1( I ) ) ) ELSE TEMP2 = MIN( ABS( D2( J )-D1( I ) ), $ ABS( D1( I )-D2( J-1 ) ) ) IF( IJOB.EQ.2 ) $ TEMP2 = TEMP2 / MAX( UNFL, ABSTOL+ULP*ABS( D1( I ) ) ) END IF TEMP1 = MAX( TEMP1, TEMP2 ) 20 CONTINUE * SSXT1 = TEMP1 RETURN * * End of SSXT1 * END