Collecting Expressions During Evaluation

The new functions Sow and Reap can be used to accumulate lists of intermediate results in an evaluation. This allows users to monitor and keep track of intermediate values of computations.

Example: Displaying Intermediate Results

Sow and Reap are used to generate a list of the steps taken during the solution of an initial value problem.

Visualizing every other step shows how NDSolve automatically adjusts the step size throughout the computation to maintain appropriate accuracy.

(Note that the plot shows every second step of the solution.)

		Documentation from The Mathematica Book Collecting Expressions During Evaluation
		Documentation from the Reference Guide Sow Reap StepMonitor