update penalty notation

Author: Carol-seven

vignettes/pen_est.qmd

@@ -210,7 +210,7 @@ $$
 ## Illustrative Visualization
 
 
-@fig-pen illustrates a comparison of various penalty functions $\lambda p(\omega)$
+@fig-pen illustrates a comparison of various penalty functions $P(\omega)$
 evaluated over a range of $\omega$ values. The main panel (right) provides
 a wider view of the penalty functions' behavior for larger $\vert\omega\vert$,
 while the inset panel (left) magnifies the region near zero $[-1, 1]$.
@@ -242,7 +242,7 @@ Illustrative penalty functions.
 :::
 
 
-@fig-deriv displays the derivative function $p^\prime(\omega)$ associated with
+@fig-deriv displays the derivative function $P^\prime(\omega)$ associated with
 a range of penalty types.
 The Lasso exhibits a constant derivative, corresponding to uniform shrinkage.
 For MCP and SCAD, the derivatives are piecewise: initially equal to the Lasso