指定した数値の指定した底での対数を返します。
Overloads Public Shared Function Log( _
ByVal a As Double, _ ByVal newBase As Double _) As Double
[C#]
public static double Log(doublea,doublenewBase);
[C++]
public: static double Log(doublea,doublenewBase);
[JScript]
public static function Log(
a : double,newBase : double) : double;
パラメータ
- a
対数を検索する対象の数値。 - newBase
対数の底。
戻り値
| a の符号 | 戻り値 |
|---|---|
| 正 | newBase ≥ 0 の場合、底 newBase での a の対数。つまり、lognewBase a 。それ以外の場合は NaN 。 |
| 0 | NegativeInfinity |
| 負 | NaN |
a が PositiveInfinity に等しく、 newBase が PositiveInfinity 、 NegativeInfinity 、または NaN に等しくない場合、このメソッドは PositiveInfinity を返します。
newBase が PositiveInfinity に等しく、 a が PositiveInfinity 、 NegativeInfinity 、または NaN に等しくない場合、このメソッドは 0 を返します。
a と newBase の両方が PositiveInfinity に等しい、または a か newBase が NaN か NegativeInfinity に等しい場合、このメソッドは NaN を返します。
解説
パラメータ a および newBase は、底 10 で指定されます。
使用例
[Visual Basic, C#, C++] 次に示すのは、 Log を使用して、選択した値から対数恒等式を求める例です。
' Example for the Math.Log( Double ) and Math.Log( Double, Double ) methods.
Imports System
Imports Microsoft.VisualBasic
Module LogDLogDD
Sub Main()
Console.WriteLine( _
"This example of Math.Log( Double ) and " + _
"Math.Log( Double, Double )" & vbCrLf & _
"generates the following output." & vbCrLf)
Console.WriteLine( _
"Evaluate these identities with selected " & _
"values for X and B (base):")
Console.WriteLine(" log(B)[X] = 1 / log(X)[B]")
Console.WriteLine(" log(B)[X] = ln[X] / ln[B]")
Console.WriteLine(" log(B)[X] = log(B)[e] * ln[X]")
UseBaseAndArg(0.1, 1.2)
UseBaseAndArg(1.2, 4.9)
UseBaseAndArg(4.9, 9.9)
UseBaseAndArg(9.9, 0.1)
End Sub 'Main
' Evaluate logarithmic identities that are functions of two arguments.
Sub UseBaseAndArg(argB As Double, argX As Double)
' Evaluate log(B)[X] = 1 / log(X)[B].
Console.WriteLine( _
vbCrLf & " Math.Log({1}, {0}) = {2:E16}" + _
vbCrLf & " 1.0 / Math.Log({0}, {1}) = {3:E16}", _
argB, argX, Math.Log(argX, argB), _
1.0 / Math.Log(argB, argX))
' Evaluate log(B)[X] = ln[X] / ln[B].
Console.WriteLine( _
" Math.Log({1}) / Math.Log({0}) = {2:E16}", _
argB, argX, Math.Log(argX) / Math.Log(argB))
' Evaluate log(B)[X] = log(B)[e] * ln[X].
Console.WriteLine( _
"Math.Log(Math.E, {0}) * Math.Log({1}) = {2:E16}", _
argB, argX, Math.Log(Math.E, argB) * Math.Log(argX))
End Sub 'UseBaseAndArg
End Module 'LogDLogDD
' This example of Math.Log( Double ) and Math.Log( Double, Double )
' generates the following output.
'
' Evaluate these identities with selected values for X and B (base):
' log(B)[X] = 1 / log(X)[B]
' log(B)[X] = ln[X] / ln[B]
' log(B)[X] = log(B)[e] * ln[X]
'
' Math.Log(1.2, 0.1) = -7.9181246047624818E-002
' 1.0 / Math.Log(0.1, 1.2) = -7.9181246047624818E-002
' Math.Log(1.2) / Math.Log(0.1) = -7.9181246047624818E-002
' Math.Log(Math.E, 0.1) * Math.Log(1.2) = -7.9181246047624804E-002
'
' Math.Log(4.9, 1.2) = 8.7166610085093179E+000
' 1.0 / Math.Log(1.2, 4.9) = 8.7166610085093161E+000
' Math.Log(4.9) / Math.Log(1.2) = 8.7166610085093179E+000
' Math.Log(Math.E, 1.2) * Math.Log(4.9) = 8.7166610085093179E+000
'
' Math.Log(9.9, 4.9) = 1.4425396251981288E+000
' 1.0 / Math.Log(4.9, 9.9) = 1.4425396251981288E+000
' Math.Log(9.9) / Math.Log(4.9) = 1.4425396251981288E+000
' Math.Log(Math.E, 4.9) * Math.Log(9.9) = 1.4425396251981288E+000
'
' Math.Log(0.1, 9.9) = -1.0043839404494075E+000
' 1.0 / Math.Log(9.9, 0.1) = -1.0043839404494075E+000
' Math.Log(0.1) / Math.Log(9.9) = -1.0043839404494075E+000
' Math.Log(Math.E, 9.9) * Math.Log(0.1) = -1.0043839404494077E+000
[C#]
// Example for the Math.Log( double ) and Math.Log( double, double ) methods.
using System;
class LogDLogDD
{
public static void Main()
{
Console.WriteLine(
"This example of Math.Log( double ) and " +
"Math.Log( double, double )\n" +
"generates the following output.\n" );
Console.WriteLine(
"Evaluate these identities with " +
"selected values for X and B (base):" );
Console.WriteLine( " log(B)[X] == 1 / log(X)[B]" );
Console.WriteLine( " log(B)[X] == ln[X] / ln[B]" );
Console.WriteLine( " log(B)[X] == log(B)[e] * ln[X]" );
UseBaseAndArg(0.1, 1.2);
UseBaseAndArg(1.2, 4.9);
UseBaseAndArg(4.9, 9.9);
UseBaseAndArg(9.9, 0.1);
}
// Evaluate logarithmic identities that are functions of two arguments.
static void UseBaseAndArg(double argB, double argX)
{
// Evaluate log(B)[X] == 1 / log(X)[B].
Console.WriteLine(
"\n Math.Log({1}, {0}) == {2:E16}" +
"\n 1.0 / Math.Log({0}, {1}) == {3:E16}",
argB, argX, Math.Log(argX, argB),
1.0 / Math.Log(argB, argX) );
// Evaluate log(B)[X] == ln[X] / ln[B].
Console.WriteLine(
" Math.Log({1}) / Math.Log({0}) == {2:E16}",
argB, argX, Math.Log(argX) / Math.Log(argB) );
// Evaluate log(B)[X] == log(B)[e] * ln[X].
Console.WriteLine(
"Math.Log(Math.E, {0}) * Math.Log({1}) == {2:E16}",
argB, argX, Math.Log(Math.E, argB) * Math.Log(argX) );
}
}
/*
This example of Math.Log( double ) and Math.Log( double, double )
generates the following output.
Evaluate these identities with selected values for X and B (base):
log(B)[X] == 1 / log(X)[B]
log(B)[X] == ln[X] / ln[B]
log(B)[X] == log(B)[e] * ln[X]
Math.Log(1.2, 0.1) == -7.9181246047624818E-002
1.0 / Math.Log(0.1, 1.2) == -7.9181246047624818E-002
Math.Log(1.2) / Math.Log(0.1) == -7.9181246047624818E-002
Math.Log(Math.E, 0.1) * Math.Log(1.2) == -7.9181246047624804E-002
Math.Log(4.9, 1.2) == 8.7166610085093179E+000
1.0 / Math.Log(1.2, 4.9) == 8.7166610085093161E+000
Math.Log(4.9) / Math.Log(1.2) == 8.7166610085093179E+000
Math.Log(Math.E, 1.2) * Math.Log(4.9) == 8.7166610085093179E+000
Math.Log(9.9, 4.9) == 1.4425396251981288E+000
1.0 / Math.Log(4.9, 9.9) == 1.4425396251981288E+000
Math.Log(9.9) / Math.Log(4.9) == 1.4425396251981288E+000
Math.Log(Math.E, 4.9) * Math.Log(9.9) == 1.4425396251981288E+000
Math.Log(0.1, 9.9) == -1.0043839404494075E+000
1.0 / Math.Log(9.9, 0.1) == -1.0043839404494075E+000
Math.Log(0.1) / Math.Log(9.9) == -1.0043839404494075E+000
Math.Log(Math.E, 9.9) * Math.Log(0.1) == -1.0043839404494077E+000
*/
[C++]
// Example for the Math::Log( double ) and Math::Log( double, double ) methods.
#using <mscorlib.dll>
using namespace System;
// Evaluate logarithmic identities that are functions of two arguments.
void UseBaseAndArg(double argB, double argX)
{
// Evaluate log(B)[X] == 1 / log(X)[B].
Console::WriteLine(
S"\n Math::Log({1}, {0}) == {2:E16}"
S"\n 1.0 / Math::Log({0}, {1}) == {3:E16}",
__box(argB), __box(argX),
__box(Math::Log(argX, argB)),
__box(1.0 / Math::Log(argB, argX)) );
// Evaluate log(B)[X] == ln[X] / ln[B].
Console::WriteLine(
S" Math::Log({1}) / Math::Log({0}) == {2:E16}",
__box(argB), __box(argX),
__box(Math::Log(argX) / Math::Log(argB)) );
// Evaluate log(B)[X] == log(B)[e] * ln[X].
Console::WriteLine(
S"Math::Log(Math::E, {0}) * Math::Log({1}) == {2:E16}",
__box(argB), __box(argX),
__box(Math::Log(Math::E, argB) * Math::Log(argX)) );
}
void main()
{
Console::WriteLine(
S"This example of Math::Log( double ) and "
S"Math::Log( double, double )\n"
S"generates the following output.\n" );
Console::WriteLine(
S"Evaluate these identities with "
S"selected values for X and B (base):" );
Console::WriteLine( S" log(B)[X] == 1 / log(X)[B]" );
Console::WriteLine( S" log(B)[X] == ln[X] / ln[B]" );
Console::WriteLine( S" log(B)[X] == log(B)[e] * ln[X]" );
UseBaseAndArg(0.1, 1.2);
UseBaseAndArg(1.2, 4.9);
UseBaseAndArg(4.9, 9.9);
UseBaseAndArg(9.9, 0.1);
}
/*
This example of Math::Log( double ) and Math::Log( double, double )
generates the following output.
Evaluate these identities with selected values for X and B (base):
log(B)[X] == 1 / log(X)[B]
log(B)[X] == ln[X] / ln[B]
log(B)[X] == log(B)[e] * ln[X]
Math::Log(1.2, 0.1) == -7.9181246047624818E-002
1.0 / Math::Log(0.1, 1.2) == -7.9181246047624818E-002
Math::Log(1.2) / Math::Log(0.1) == -7.9181246047624818E-002
Math::Log(Math::E, 0.1) * Math::Log(1.2) == -7.9181246047624804E-002
Math::Log(4.9, 1.2) == 8.7166610085093179E+000
1.0 / Math::Log(1.2, 4.9) == 8.7166610085093161E+000
Math::Log(4.9) / Math::Log(1.2) == 8.7166610085093179E+000
Math::Log(Math::E, 1.2) * Math::Log(4.9) == 8.7166610085093179E+000
Math::Log(9.9, 4.9) == 1.4425396251981288E+000
1.0 / Math::Log(4.9, 9.9) == 1.4425396251981288E+000
Math::Log(9.9) / Math::Log(4.9) == 1.4425396251981288E+000
Math::Log(Math::E, 4.9) * Math::Log(9.9) == 1.4425396251981288E+000
Math::Log(0.1, 9.9) == -1.0043839404494075E+000
1.0 / Math::Log(9.9, 0.1) == -1.0043839404494075E+000
Math::Log(0.1) / Math::Log(9.9) == -1.0043839404494075E+000
Math::Log(Math::E, 9.9) * Math::Log(0.1) == -1.0043839404494077E+000
*/
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をクリックします。
必要条件
プラットフォーム: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 ファミリ, Common Language Infrastructure (CLI) Standard