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// Copyright ©2015 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gonum
import (
"math"
"gonum.org/v1/gonum/lapack"
)
// Dlascl multiplies an m×n matrix by the scalar cto/cfrom.
//
// cfrom must not be zero, and cto and cfrom must not be NaN, otherwise Dlascl
// will panic.
//
// Dlascl is an internal routine. It is exported for testing purposes.
func (impl Implementation) Dlascl(kind lapack.MatrixType, kl, ku int, cfrom, cto float64, m, n int, a []float64, lda int) {
switch kind {
default:
panic(badMatrixType)
case 'H', 'B', 'Q', 'Z': // See dlascl.f.
panic("not implemented")
case lapack.General, lapack.UpperTri, lapack.LowerTri:
if lda < max(1, n) {
panic(badLdA)
}
}
switch {
case cfrom == 0:
panic(zeroCFrom)
case math.IsNaN(cfrom):
panic(nanCFrom)
case math.IsNaN(cto):
panic(nanCTo)
case m < 0:
panic(mLT0)
case n < 0:
panic(nLT0)
}
if n == 0 || m == 0 {
return
}
switch kind {
case lapack.General, lapack.UpperTri, lapack.LowerTri:
if len(a) < (m-1)*lda+n {
panic(shortA)
}
}
smlnum := dlamchS
bignum := 1 / smlnum
cfromc := cfrom
ctoc := cto
cfrom1 := cfromc * smlnum
for {
var done bool
var mul, ctol float64
if cfrom1 == cfromc {
// cfromc is inf.
mul = ctoc / cfromc
done = true
ctol = ctoc
} else {
ctol = ctoc / bignum
if ctol == ctoc {
// ctoc is either 0 or inf.
mul = ctoc
done = true
cfromc = 1
} else if math.Abs(cfrom1) > math.Abs(ctoc) && ctoc != 0 {
mul = smlnum
done = false
cfromc = cfrom1
} else if math.Abs(ctol) > math.Abs(cfromc) {
mul = bignum
done = false
ctoc = ctol
} else {
mul = ctoc / cfromc
done = true
}
}
switch kind {
case lapack.General:
for i := 0; i < m; i++ {
for j := 0; j < n; j++ {
a[i*lda+j] = a[i*lda+j] * mul
}
}
case lapack.UpperTri:
for i := 0; i < m; i++ {
for j := i; j < n; j++ {
a[i*lda+j] = a[i*lda+j] * mul
}
}
case lapack.LowerTri:
for i := 0; i < m; i++ {
for j := 0; j <= min(i, n-1); j++ {
a[i*lda+j] = a[i*lda+j] * mul
}
}
}
if done {
break
}
}
}
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