linalg.go

     1  // Copyright 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package linalg
     6  
     7  import "math"
     8  
     9  // Numeric is type bound that matches any numeric type.
    10  // It would likely be in a constraints package in the standard library.
    11  type Numeric interface {
    12  	~int | ~int8 | ~int16 | ~int32 | ~int64 |
    13  		uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
    14  		float32 | ~float64 |
    15  		complex64 | ~complex128
    16  }
    17  
    18  func DotProduct[T Numeric](s1, s2 []T) T {
    19  	if len(s1) != len(s2) {
    20  		panic("DotProduct: slices of unequal length")
    21  	}
    22  	var r T
    23  	for i := range s1 {
    24  		r += s1[i] * s2[i]
    25  	}
    26  	return r
    27  }
    28  
    29  // NumericAbs matches numeric types with an Abs method.
    30  type NumericAbs[T any] interface {
    31  	Numeric
    32  
    33  	Abs() T
    34  }
    35  
    36  // AbsDifference computes the absolute value of the difference of
    37  // a and b, where the absolute value is determined by the Abs method.
    38  func AbsDifference[T NumericAbs[T]](a, b T) T {
    39  	d := a - b
    40  	return d.Abs()
    41  }
    42  
    43  // OrderedNumeric is a type bound that matches numeric types that support the < operator.
    44  type OrderedNumeric interface {
    45  	~int | ~int8 | ~int16 | ~int32 | ~int64 |
    46  		uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
    47  		float32 | ~float64
    48  }
    49  
    50  // Complex is a type bound that matches the two complex types, which do not have a < operator.
    51  type Complex interface {
    52  	~complex64 | ~complex128
    53  }
    54  
    55  // OrderedAbs is a helper type that defines an Abs method for
    56  // ordered numeric types.
    57  type OrderedAbs[T OrderedNumeric] T
    58  
    59  func (a OrderedAbs[T]) Abs() OrderedAbs[T] {
    60  	if a < 0 {
    61  		return -a
    62  	}
    63  	return a
    64  }
    65  
    66  // ComplexAbs is a helper type that defines an Abs method for
    67  // complex types.
    68  type ComplexAbs[T Complex] T
    69  
    70  func (a ComplexAbs[T]) Abs() ComplexAbs[T] {
    71  	r := float64(real(a))
    72  	i := float64(imag(a))
    73  	d := math.Sqrt(r * r + i * i)
    74  	return ComplexAbs[T](complex(d, 0))
    75  }
    76  
    77  func OrderedAbsDifference[T OrderedNumeric](a, b T) T {
    78  	return T(AbsDifference(OrderedAbs[T](a), OrderedAbs[T](b)))
    79  }
    80  
    81  func ComplexAbsDifference[T Complex](a, b T) T {
    82  	return T(AbsDifference(ComplexAbs[T](a), ComplexAbs[T](b)))
    83  }
    84
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