What is New in Mathematica 5.1 Products
-----
 /
Mathematica
*String Manipulation
*DatabaseLink
*Binary Data I/O
*Additional Import/Export Formats
*Web Services
*Large-Scale Graph Layout
*Array Plotting
*Enhanced Linear Algebra Performance
*Piecewise
<Integration over Regions
*Event Handling
*Symbolic Differential Equations
*Cluster Analysis
*EquationTrekker
*MathematicaMark2004
*GUIKit
*Summary of Features
*Ask about this page
PreviousNext

Integration over Implicitly Defined Regions

See What's New in Wolfram Mathematica 6

Regions defined by inequalities or piecewise functions can now be integrated symbolically or numerically by Mathematica--a unique capability developed at Wolfram Research. The functions Integrate and NIntegrate both automatically handle regions implicitly defined by arbitrary logical combinations of polynomial inequalities, as well as many transcendental inequalities.

Cases covered include:

  • Regions defined by multivariate polynomial inequalities
  • Problems over transcendental regions (where solvable)
  • Integrable regions involving infinite ranges
  • Undefined parameters in the region specification (solutions are generated for all possible values)




More Details    

Example: Integration over the Unit Disk

This computes the area of the unit disk using symbolic integration. Boole is a new function that converts inequalities to Boolean expressions.

In[1]:=

Out[1]:=


The region represented
by x2+ y2 < 1

This computes the same area using numeric methods, but using a similar symbolic reduction method as for the symbolic integral.

In[2]:=NIntegrate[Boole[x^2 + y^2<1], {x, -∞, ∞}, {y,
-∞, ∞}]

Out[2]:=3.14159



Example: Integration over Combinations of Inequalities

You can use any logical combination of inequalities and integrate a function over that region.

In[3]:=∫_
(-∞)^∞∫_ (-∞)^∞ (y^4 + x^2) Boole[x^2 +
y^2<1∧x<y] yx

Out[3]:=(3 π)/16



Example: Integration over Parameterized Inequalities

With undefined parameters in the region description, the result is computed for all possible values.

In[4]:=∫_
(-1)^1∫_ (-1)^1Boole[a x^2 + y^2<1] yx

Out[4]:=

Using the symbolic result above, the region and its area are plotted for different values of parameter a.

Representation of regionArea of region represented



Example: Integration over an Infinite Collection of Intervals

The methods work for all regions described by polynomial inequalities, but also for many solvable regions described by transcendental inequalities.

In this case the integration is over an infinite collection of intervals.

In[5]:=∫_
(-∞)^∞Boole[1/2<sin(x) <2/3]/x^2x

Out[5]:=(ψ^(0)(tan^(-1)(2/5^(1/2))/(2 π)) + ψ^(0)(tan^(-1)(2/5^(1/2))/(2 π) + 1/2) ... 0)(1/2 - tan^(-1)(2/5^(1/2))/(2 π)) + 2 3^(1/2) π)/((-1 + 3^(1/2)) (1 + 3^(1/2)) π)


Related Links

Tutorials from The Mathematica Book Tutorials from The Mathematica Book
Integrals over Regions
  
Built-In Functions Reference Guide  Built-In Functions Reference Guide
Boole
Integrate
NIntegrate
Piecewise
UnitStep
 
Additional Information  Additional Information
Technical Presentation: Solving Systems of Equations and Inequalities over Specified Domains


Back to Top PreviousNext



 © 2008 Wolfram Research, Inc.  Terms of Use  Privacy Policy | [ja]