Lasso Soft Threshold

Apply the soft-thresholding operator used by one coordinate-descent step of the lasso: shrink the value z toward zero by lam, and set it to exactly zero if $\mathrm{\mid }z\mathrm{\mid }\le \lambda |z|\backslash le\backslash lambda$.

Implement solve(z,lam).

Returns. Return the shrunken value as a float (0.0 when it is thresholded away). lam must be non-negative.

Examples

Example 1

Input:

solve(3.0, 1.0)

Output:

2.0

Example 2

Input:

solve(-2.5, 1.0)

Output:

-1.5

Example 3

Input:

solve(0.4, 1.0)

Output:

0.0