+ ex bipoly;
+
+ for (unsigned i1=0; i1<=degree; ++i1)
+ for (unsigned i2=0; i2<=degree-i1; ++i2)
+ bipoly += numeric((rand()-RAND_MAX/2))*pow(x1,i1)*pow(x2,i2);
+
+ return bipoly;
+}
+
+/* Chose a random symbol or number from the argument list. */
+const ex
+random_symbol(const symbol & x,
+ const symbol & y,
+ const symbol & z,
+ bool rational = true,
+ bool complex = false)
+{
+ ex e;
+ switch (abs(rand()) % 4) {
+ case 0:
+ e = x;
+ break;
+ case 1:
+ e = y;
+ break;
+ case 2:
+ e = z;
+ break;
+ case 3: {
+ int c1;
+ do { c1 = rand()%20 - 10; } while (!c1);
+ int c2;
+ do { c2 = rand()%20 - 10; } while (!c2);
+ if (!rational)
+ c2 = 1;
+ e = numeric(c1, c2);
+ if (complex && !(rand()%5))
+ e = e*I;
+ break;
+ }
+ }
+ return e;
+}
+
+/* Create a sparse random tree in three symbols. */
+const ex
+sparse_tree(const symbol & x,
+ const symbol & y,
+ const symbol & z,
+ int level,
+ bool trig = false, // true includes trigonometric functions
+ bool rational = true, // false excludes coefficients in Q
+ bool complex = false) // true includes complex numbers
+{
+ if (level == 0)
+ return random_symbol(x,y,z,rational,complex);
+ switch (abs(rand()) % 10) {
+ case 0:
+ case 1:
+ case 2:
+ case 3:
+ return add(sparse_tree(x,y,z,level-1, trig, rational),
+ sparse_tree(x,y,z,level-1, trig, rational));
+ case 4:
+ case 5:
+ case 6:
+ return mul(sparse_tree(x,y,z,level-1, trig, rational),
+ sparse_tree(x,y,z,level-1, trig, rational));
+ case 7:
+ case 8: {
+ ex powbase;
+ do {
+ powbase = sparse_tree(x,y,z,level-1, trig, rational);
+ } while (powbase.is_zero());
+ return pow(powbase, abs(rand() % 4));
+ break;
+ }
+ case 9:
+ if (trig) {
+ switch (abs(rand()) % 4) {
+ case 0:
+ return sin(sparse_tree(x,y,z,level-1, trig, rational));
+ case 1:
+ return cos(sparse_tree(x,y,z,level-1, trig, rational));
+ case 2:
+ return exp(sparse_tree(x,y,z,level-1, trig, rational));
+ case 3: {
+ ex logex;
+ do {
+ ex logarg;
+ do {
+ logarg = sparse_tree(x,y,z,level-1, trig, rational);
+ } while (logarg.is_zero());
+ // Keep the evaluator from accidentally plugging an
+ // unwanted I in the tree:
+ if (!complex && logarg.info(info_flags::negative))
+ logarg = -logarg;
+ logex = log(logarg);
+ } while (logex.is_zero());
+ return logex;
+ break;
+ }
+ }
+ } else
+ return random_symbol(x,y,z,rational,complex);
+ }
+
+ return 0;