added NaN test for squared_distance
added NaN test for tcrossprod
added NaN test for divide
added NaN test for multiply
added NaN test for singular_values
Added expect_matrix_nan for std::vector
added NaN test for fill
added NaN test for diagonal
added NaN test for diag_matrix
added NaN test for accumulator
added NaN test for cumulative_sum
Added function expect_matrix_eq_or_both_nan
added NaN test for assign
Fix multiply_test
added NaN test for initialize
added NaN test for cholesky_decompose
added NaN test for inverse_spd
added NaN test for minus