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more precise hardcoded const for erf and selu #1408

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more precise hardcoded const for erf and selu #1408

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6 changes: 3 additions & 3 deletions tinygrad/mixin/elementwise.py
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Original file line number Diff line number Diff line change
Expand Up @@ -985,7 +985,7 @@ def celu(self, alpha=1.0) -> Self:
"""
return alpha * (self / alpha).elu()

def selu(self, alpha=1.67326, gamma=1.0507) -> Self:
def selu(self, alpha=1.6732632423543772, gamma=1.0507009873554805) -> Self:
"""
Applies the Scaled Exponential Linear Unit (SELU) function element-wise.

Expand Down Expand Up @@ -1065,9 +1065,9 @@ def erf(self) -> Self:
print(Tensor([-1.5, -1.0, -0.5, 0., 0.5, 1.0, 1.5]).erf().numpy())
```
"""
# https://personal.math.ubc.ca/~cbm/aands/page_299.htm 7.1.26
# https://personal.math.ubc.ca/~cbm/aands/page_299.htm 7.1.26, with a1 rounded so the coefficients sum to 1 and erf(0) is exactly 0
t = 1.0 / (1.0 + 0.3275911 * (s:=(self >= 0).where(1.0, -1.0)) * self)
return s * (1.0 - t * polyN(t, [1.061405429, -1.453152027, 1.421413741, -0.284496736, 0.254829592]) * (-self.square()).exp())
return s * (1.0 - t * polyN(t, [1.061405429, -1.453152027, 1.421413741, -0.284496736, 0.254829593]) * (-self.square()).exp())

def softsign(self) -> Self:
"""
Expand Down