metric_field.md
In ricci: Ricci Calculus

validation works

Code
  metric_field(array("a", c(1, 1)), array("1/a", c(1, 1)), "b")
Condition
  Error in `metric_field()`:
  ! Expression in `metric` is not solely a function of coordinates sepcified in `coords`.
  i The expression in `metric` can only depend on coordinates, not on other parameters. When evaluted at a point (specified by coorindates) the expression needs to yield a number.
  Caused by error:
  ! object 'a' not found

Code
  metric_field(array("a", c(1, 1)), array(c("1/a", "b"), c(1, 2)), "a")
Condition
  Error in `metric_field()`:
  ! Argument `metric_inv` is not a valid array.
  i A quadratic (n by n) matrix/array is required.

Code
  metric_field(array("a", c(1, 1)), array(1:4, c(2, 2)), "a")
Condition
  Error in `metric_field()`:
  ! Matrix dimensions of `metric` does not match matrix dimensions of `metric_inv`.
  i `metric_inv` needs to be the inverse matrix of `metric`.

Code
  metric_field(array("a(", c(1, 1)), array("a", c(1, 1)), "a")
Condition
  Error in `metric_field()`:
  ! Invalid expression.
  i Argument `metric` needs to contain valid R expressions.
  Caused by error in `parse()`:
  ! <text>:2:0: unexpected end of input
  1: a(
     ^

Code
  metric_field(array(1:6, c(2, 3)), array(1:6, c(2, 3)), "a")
Condition
  Error in `metric_field()`:
  ! Argument `metric` is not a valid array.
  i A quadratic (n by n) matrix/array is required.

Code
  metric_field(array("a(", c(1, 1)), array("a", c(1, 1)), 3)
Condition
  Error in `metric_field()`:
  ! Argument `coords` is no character vector.

Code
  metric_field(array("a(", c(1, 1)), array("a", c(1, 1)), c("a", "b"))
Condition
  Error in `metric_field()`:
  ! Dimension and length of `metric` and `coords` are incompatible.
  i The length of `coords` needs to match the array dimension of `metric`.