fix: Initialize residuals when initializing simplex in Nelder-Mead

src/solver/nelder_mead.rs

@@ -233,15 +233,16 @@ where
 
  // It is important to return early on error before the point is
  // added to the simplex.
- let mut error_best = f.apply(x)?;
+ let mut error_best = f.apply_eval(x, fx)?;
+ fx_best.copy_from(fx);
  errors.push(error_best);
  simplex.push(x.clone_owned());
 
  for j in 0..n {
  let mut xi = x.clone_owned();
  xi[j] = dom.vars()[j].clamp(xi[j] + scale[j]);
 
- let error = match f.apply(&xi) {
+ let error = match f.apply_eval(&xi, fx) {
  Ok(error) => error,
  // Do not fail when invalid value is encountered during
  // building the simplex. Instead, treat it as infinity so