# rrsigma

Compute relative density ratio

## Syntax

```s = rrsigma(rho, mach, g) ```

## Description

`s = rrsigma(rho, mach, g)` computes `m` density relative ratios, `s`, from `m` static densities, `rho`, `m` Mach numbers, `mach`, and `m` specific heat ratios, `g`. `rho` must be in kilograms per meter cubed.

## Examples

Determine the relative density ratio for three densities:

```sigma = rrsigma([1.225 0.3639 0.0953], 0.5, 1.4) sigma = 1.1297 0.3356 0.0879```

Determine the relative density ratio for three densities and three different heat ratios:

```sigma = rrsigma([1.225 0.3639 0.0953], 0.5, [1.4 1.35 1.4]) sigma = 1.1297 0.3357 0.0879```

Determine the relative density ratio for three densities at three different conditions:

```sigma = rrsigma([1.225 0.3639 0.0953], [0.5 1 2], [1.4 1.35 1.4]) sigma = 1.1297 0.4709 0.3382```

## Assumptions and Limitations

For cases in which total density ratio is desired (Mach number is nonzero), the total density is calculated assuming perfect gas (with constant molecular weight, constant pressure specific heat, and constant specific heat ratio) and dry air.

## References

Aeronautical Vestpocket Handbook, United Technologies Pratt & Whitney, August, 1986 