Binorm {VGAM} | R Documentation

## Bivariate Normal Distribution Cumulative Distribution Function

### Description

Density, cumulative distribution function and random generation for the bivariate normal distribution distribution.

### Usage

    dbinorm(x1, x2, mean1 = 0, mean2 = 0, var1 = 1, var2 = 1, cov12 = 0, log = FALSE)
    pbinorm(q1, q2, mean1 = 0, mean2 = 0, var1 = 1, var2 = 1, cov12 = 0)
    rbinorm(n,      mean1 = 0, mean2 = 0, var1 = 1, var2 = 1, cov12 = 0)
     pnorm2(x1, x2, mean1 = 0, mean2 = 0, var1 = 1, var2 = 1, cov12 = 0)

### Arguments

`x1, x2, q1, q2` | vector of quantiles.
`mean1, mean2, var1, var2, cov12` | vector of means, variances and the covariance.

`n` | number of observations. Same as `rnorm`.
`log` | Logical. If `log = TRUE` then the logarithm of the density is returned.

### Details

The default arguments correspond to the standard bivariate normal distribution with correlation parameter rho = 0. That is, two independent standard normal distributions. Let `sd1` (say) be `sqrt(var1)` and written sigma_1, etc. Then the general formula for the correlation coefficient is rho = cov / (sigma_1 * sigma_2) where cov is argument `cov12`. Thus if arguments `var1` and `var2` are left alone then `cov12` can be inputted with rho.

One can think of this function as an extension of `pnorm` to two dimensions, however note that the argument names have been changed for VGAM 0.9-1 onwards.

### Value

`dbinorm` gives the density, `pbinorm` gives the cumulative distribution function, `rbinorm` generates random deviates (n by 2 matrix).

### Warning

Being based on an approximation, the results of `pbinorm()` may be negative! Also, `pnorm2()` should be withdrawn soon; use `pbinorm()` instead because it is identical.

### Note

For `rbinorm()`, if the ith variance-covariance matrix is not positive-definite then the ith row is all `NA`s.

### References

`pbinorm()` is based on Donnelly (1973), the code was translated from FORTRAN to ratfor using struct, and then from ratfor to C manually. The function was originally called `bivnor`, and TWY only wrote a wrapper function.

Donnelly, T. G. (1973) Algorithm 462: Bivariate Normal Distribution. Communications of the ACM, 16, 638.

### See Also

`pnorm`, `binormal`, `uninormal`.

### Examples

    yvec <- c(-5, -1.96, 0, 1.96, 5)
    ymat <- expand.grid(yvec, yvec)
    cbind(ymat, pbinorm(ymat[, 1], ymat[, 2]))

    ## Not run:  rhovec <- seq(-0.95, 0.95, by = 0.01)
    plot(rhovec, pbinorm(0, 0, cov12 = rhovec), type = "l", col = "blue", las = 1)
    abline(v = 0, h = 0.25, col = "gray", lty = "dashed")
    ## End(Not run)

[Package VGAM version 1.0-3 Index]