You can, by transforming it, similar to Linearizing non-linear models by transformation. Something along the lines of the following should work:

```
double[] Exponential(double[] x, double[] y,
DirectRegressionMethod method = DirectRegressionMethod.QR)
{
double[] y_hat = Generate.Map(y, Math.Log);
double[] p_hat = Fit.LinearCombination(x, y_hat, method, t => 1.0, t => t);
return new[] {Math.Exp(p_hat[0]), p_hat[1]};
}
```

Example usage:

```
double[] x = new[] { 1.0, 2.0, 3.0 };
double[] y = new[] { 2.0, 4.1, 7.9 };
double[] p = Exponential(x,y); // a=1.017, r=0.687
double[] yh = Generate.Map(x,k => p[0]*Math.Exp(p[1]*k)) // 2.02, 4.02, 7.98
```