solve_leastsq.py:mkestimate(): ignore 0 delay rows, assert non-trivial seed

Signed-off-by: John McMaster <johndmcmaster@gmail.com>

fuzzers/007-timing/solve_leastsq.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 
-from timfuz import Benchmark, load_sub, corner_s2i, acorner2csv
+from timfuz import Benchmark, load_sub
 import timfuz
 import numpy as np
 import math
@@ -22,11 +22,20 @@ def mkestimate(Anp, b):
     x0 = np.array([1e3 for _x in range(cols)])
     for row_np, row_b in zip(Anp, b):
         for coli, val in enumerate(row_np):
-            if val:
-                # Scale by number occurances
-                ub = row_b / val
-                if ub >= 0:
-                    x0[coli] = min(x0[coli], ub)
+            # favor non-trivial values
+            if val <= 0:
+                continue
+            # Scale by number occurances
+            ub = row_b / val
+            if ub <= 0:
+                continue
+            if x0[coli] == 0:
+                x0[coli] = ub
+            else:
+                x0[coli] = min(x0[coli], ub)
+    # reject solutions that don't provide a seed value
+    # these lead to bad optimizations
+    assert sum(x0) != 0
     return x0