## Power Calculation for Two Coprimary Endpoints.

### Usage

```CopriEndpt.Power(n, tau, mu1, mu2, rho, alpha1, alpha2, alternative)
```

### Arguments

 `n` sample size for the design. `tau` information time for the interim analysis. `mu1` mean value for coprimary endpoint 1. `mu2` mean value for coprimary endpoint 2. `rho` correlation coefficient between two coprimary endpoints. `alpha1` significant level for the first stage. `alpha2` significant level for the second stage. `alternative` indicates the alternative hypothesis and must be one of `"two.sided"` or `"two.sided"`.

### Value

The evaluated power with attributes and computational error.

Yalin Zhu

### References

Chang, M. (2014). Adaptive design theory and implementation using SAS and R. CRC Press.

### Examples

```# Example in Chang (2014) page  272
CopriEndpt.Power(n=197, tau=0.5, mu1=0.2, mu2=0.2, rho=0.5,
alpha1=0.0025, alpha2=0.024, alternative="one.sided")
sapply(c(-0.8,-0.5,-0.2,0,0.2,0.5,0.8),CopriEndpt.Power,
n=197, tau=0.5, mu1=0.2, mu2=0.2, alpha1=0.0025, alpha2=0.024, alternative="one.sided")
```