readme: add exercise 7

README.md

@@ -131,3 +131,22 @@ perform optimally in this case.
 The `-c` and `-d` options controls whether the convolved or deconvolved
 histogram counts should be printed to `stdout`. For more options
 run the program with `-h` to see the usage screen.
+
+
+### Exercise 7
+
+`ex-7/bin/main` generates a sample with two classes of 2D points (signal,
+noise) and trains either a Fisher linear discriminant or a single perceptron to
+classify them (`-m` argument to change mode). Alternatively the weights can be
+set manually via the `-w` argument. In either case the program then prints the
+classified data in this order: signal then noise.
+
+To plot the result of the linear classification pipe the output to
+`ex-7/plot.py`. The program generates two figures:
+  - a scatter plot showing the Fisher projection line and the cut line
+  - two histograms of the projected data and the cut line
+
+`ex-7/bin/test` takes a model trained in `ex-7/bin/main` and test it against
+newly generated datasets (`-i` to set the number of test iterations). The
+program prints the statistics of the number of false positives, false
+negatives and finally the purity and efficiency of the classification.