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What's New in Mathematica 5
Numeric Computations NDSolve The function NDSolve has been completely rewritten, resulting in better performance and much greater flexibility. While many of the enhancements are transparent and will benefit all users, the new NDSolve gives advanced users many more options for selecting methods, setting evaluation options, and monitoring the progress of the solver—and even ways for implementing their own custom solvers into NDSolve. Some of the most significant improvements include:
Example: Solving a System of Differential Equations The following example demonstrates the use of vector variables to specify a system of differential equations of dimension 12. To assist in the visualization of the results of the following numerical differential equation, it is useful to view the solution as a threedimensional graphic.
The following example is of a space curve defined by curvature and torsion.
Example: Solving a Matrix Differential Equation In this example we solve the matrix differential equation with and the initial condition .
We can define a particular matrix norm and look at the differences.
Example: Solving a DifferentialAlgebraic Equation In this case we have one differential equation and one explicit algebraic equation . Notice how (in this case only) we give one initial value equation . The initial value equation for is implicitly determined by the algebraic equation.
Example: Modeling an Exothermic Chemical Reactor The following is an exothermal chemical reactor model. In this simple firstorder isomerization process, the heat is removed through an external cooling circuit. In this case we have product concentration, product temperature, and reaction rate. Furthermore, we have reactant concentration, reactant temperature, cooling circuit temperature, and constants.
Example: Solving a Partial Differential Equation A soliton is a solitary wave that survives collisions with other solitary waves. For example, ocean waves are solitons. The Kortewegde Vries equation was the first differential equation describing a soliton. Technical applications of solitons include longhaul optical fiber transmission systems. This is the Kortewegde Vries equation in one spatial dimension.
This is a solitary wave solution to the KdV equation above.
Because we are going to use periodic boundary conditions, we will add up all the period contributions to get the following initial condition.
Here we can see how these solitary waves interact.
Notice the nonlinear interaction when they pass each other.
FindRoot The function FindRoot now supports general array variables and includes new and improved algorithms that lead to speed increases and better handling of largescale problems on computers with limited memory. Example: Solving a Matrix Riccati Equation Here is an example of solving a matrix equation—in this case a continuoustime algebraic Riccati equation . Suppose we have a system (e.g., a double integrator, or some type of mechanical system) and constraints.
This finds a matrix root to the equation .
FindFit The new function FindFit supersedes and extends the functionality of the functions Fit and NonlinearFit. FindFit supports array variables, provides more methods, and can use the functions StepMonitor and EvaluationMonitor for keeping track of the process. Example: Fitting Data FindFit can even fit data using a piecewise continuous function.
The data can be shown with the following fitting function.
Example: Fitting a Circle Suppose we are taking measurements along a circle.
This fits a circle with radius and center to the data.
This shows the data and the fitted circle together.
FindMinimum and FindMaximum The new function FindMaximum has been added for convenience. The functions FindMinimum and FindMaximum now support general array variables, offer new and improved algorithms, and work better in limitedmemory situations. Example: Computing a Matrix Norm In this case we are using a vector variable.


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