switch 'math' to 'numpy'
switch 'math' to 'numpy'


Former-commit-id: 476e65b8b3a5724ebe5c24509790113c96153c30 [formerly 5c964abb1f9b8dccd1f1a85cd24b8748bcee4bfe]
Former-commit-id: c3a5cdf7d477fbc2c7ef56d4bcbd2d02fa0f16d8
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine