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131 lines
3.3 KiB
Go
131 lines
3.3 KiB
Go
// Copyright ©2017 The gonum Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package mat_test
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import (
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"fmt"
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"gonum.org/v1/gonum/mat"
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)
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func ExampleDense_Add() {
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// Initialize two matrices, a and b.
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a := mat.NewDense(2, 2, []float64{1, 0, 1, 0})
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b := mat.NewDense(2, 2, []float64{0, 1, 0, 1})
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// Add a and b, placing the result into c.
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// ...Notice that the size is automatically adjusted when the receiver has zero size.
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var c mat.Dense
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c.Add(a, b)
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// Print the result using the formatter.
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fc := mat.Formatted(&c, mat.Prefix(" "), mat.Squeeze())
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fmt.Printf("Result:\nc = %v\n\n", fc)
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// Output:
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// Result:
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// c = ⎡1 1⎤
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// ⎣1 1⎦
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//
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}
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func ExampleDense_Sub() {
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// Initialize two matrices, a and b.
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a := mat.NewDense(2, 2, []float64{1, 1, 1, 1})
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b := mat.NewDense(2, 2, []float64{1, 0, 0, 1})
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// Subtract b from a, placing the result into a.
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a.Sub(a, b)
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// Print the result using the formatter.
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fa := mat.Formatted(a, mat.Prefix(" "), mat.Squeeze())
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fmt.Printf("Result:\na = %v\n\n", fa)
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// Output:
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// Result:
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// a = ⎡0 1⎤
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// ⎣1 0⎦
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//
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}
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func ExampleDense_MulElem() {
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// Initialize two matrices, a and b.
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a := mat.NewDense(2, 2, []float64{1, 2, 3, 4})
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b := mat.NewDense(2, 2, []float64{1, 2, 3, 4})
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// Multiply the elements of a and b, placing the result into a.
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a.MulElem(a, b)
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// Print the result using the formatter.
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fa := mat.Formatted(a, mat.Prefix(" "), mat.Squeeze())
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fmt.Printf("Result:\na = %v\n\n", fa)
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// Output:
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// Result:
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// a = ⎡1 4⎤
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// ⎣9 16⎦
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//
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}
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func ExampleDense_DivElem() {
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// Initialize two matrices, a and b.
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a := mat.NewDense(2, 2, []float64{5, 10, 15, 20})
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b := mat.NewDense(2, 2, []float64{5, 5, 5, 5})
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// Divide the elements of a by b, placing the result into a.
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a.DivElem(a, b)
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// Print the result using the formatter.
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fa := mat.Formatted(a, mat.Prefix(" "), mat.Squeeze())
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fmt.Printf("Result:\na = %v\n\n", fa)
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// Output:
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// Result:
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// a = ⎡1 2⎤
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// ⎣3 4⎦
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//
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}
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func ExampleDense_Inverse() {
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// Initialize two matrices, a and ia.
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a := mat.NewDense(2, 2, []float64{4, 0, 0, 4})
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var ia mat.Dense
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// Take the inverse of a and place the result in ia.
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ia.Inverse(a)
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// Print the result using the formatter.
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fa := mat.Formatted(&ia, mat.Prefix(" "), mat.Squeeze())
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fmt.Printf("Result:\nia = %.2g\n\n", fa)
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// Confirm that A * A^-1 = I
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var r mat.Dense
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r.Mul(a, &ia)
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fr := mat.Formatted(&r, mat.Prefix(" "), mat.Squeeze())
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fmt.Printf("Result:\nr = %v\n\n", fr)
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// The Inverse operation, however, is numerically unstable, and should typically be avoided.
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// For example, a common need is to find x = A^-1 * b. In this case, the SolveVec method of VecDense
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// (if b is a Vector) or Solve method of Dense (if b is a matrix) should used instead of computing
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// the Inverse of A.
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b := mat.NewDense(2, 2, []float64{2, 0, 0, 2})
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var x mat.Dense
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x.Solve(a, b)
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// Print the result using the formatter.
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fx := mat.Formatted(&x, mat.Prefix(" "), mat.Squeeze())
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fmt.Printf("Result:\nx = %v\n\n", fx)
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// Output:
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// Result:
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// ia = ⎡0.25 -0⎤
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// ⎣ 0 0.25⎦
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//
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// Result:
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// r = ⎡1 0⎤
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// ⎣0 1⎦
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//
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// Result:
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// x = ⎡0.5 0⎤
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// ⎣ 0 0.5⎦
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//
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}
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