fold | R Documentation |

Fold a square matrix by collapsing lower triangle on upper triangle, or vice versa, through addition.

fold(x, direction = c("upper", "lower"))

`x` |
square numeric matrix |

`direction` |
character, one of |

By default, for `direction=="upper"`

, the function takes the values in
the lower triangle of `x`

and adds them symetrically to the values in
the upper triangle. The values on the diagonal remain unchanged. The lower
triangle is filled with 0s. If `direction=="lower"`

the upper triangle
is collapsed on to the lower triangle.

Square matrix of the same `dim`

as `x`

with the lower
(upper) triangle folded onto the upper (lower) triangle.

`upper.tri()`

, `lower.tri()`

, `symmetrize()`

(m <- matrix(1:4, 2, 2)) (f1 <- fold(m)) (f2 <- fold(m, "lower")) stopifnot( all.equal(diag(m), diag(f1)) ) stopifnot( all.equal(diag(m), diag(f2)) ) stopifnot( all.equal(f1[1,2], m[2,1] + m[1,2]) ) stopifnot( all.equal(f2[2,1], m[2,1] + m[1,2]) )

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