Covariance set

**Return Type**`A::return_type`The type of

*C*_{i, j}(,) (see definition above).**Argument Type**`A::argument_type`The type of location

**u**(see definition above).

a | an object of a type that models Covariance set | |

U | a type that models Location | |

u1,u2 | objects of type U | |

i, j | objects of type convertible to unsigned int |

**Set-up the system**`a(i,j, u1,u2)`Return type: a type convertible to `double`Semantics: returns the covariance value *C*_{i, j}(,)

`LMC_covariance``MM1_covariance``MM2_covariance`