### LON-CAPA Help

As you may know, it is extremely difficult to determine whether a given expression is exactly equal to another expression in general. For example, is sin2x=2sinxcosx? LON-CAPA has two ways of finding out if it is:

• algebraically, using a symbolic algebra system

• numerically, using sampling points

You need to determine which way is the safest in a given situation.

If you don't specify sampling points, the symbolic algebra system is used.

If you do specify sampling points, LON-CAPA uses them. If your answer and the student's answer agree at the sampling points within your given tolerance factor, the student's answer will be accepted. If the student's answer does not agree at the sampling points within your given tolerance factor, it will be rejected.

To specify where to sample the formulas for determining whether the student's answer is correct, you need to put a sampling specification in the Sample Points field. The sampling specifications take the following format:

1. A comma-separated list of the variables you wish to interpret,

2. followed by "@" (not in quotes),

3. followed by any number of the following two things, separated by semi-colons:

1. a comma-separated list of as many numbers as there are variables, which specifies one sampling point, OR

2. a comma-separated list of as many numbers as there are variables, followed by a colon, followed by another list of as many numbers as there are variables, followed by a #, followed by an integer.

The first form specifies one point to sample. The second form specifies a range for each variable, and the system will take as many random samples from that range as the number after the #.

For 2x2+4, with one variable "x", one could specify:

• "x@2", which will sample the answers only at 2. (This is generally a bad idea, as the student could get lucky and match at that point)

• "x@1:5#4" will takes 4 samples from somewhere between 1 and 5.

• "x@1:5#4;10" will takes 4 samples from somewhere between 1 and 5, and also sample at 10.

For 2x2+3y3+z, which has three variables, one could specify:

• "x,y,z@4,5,3:10,12,8#4;0,0,0", which take four samples from the box determined by the points (4, 5, 3) and (10, 12, 8), and also sample the point (0, 0, 0).