Report factor value bytes and preserve overflow-safe reduction limits

crates/solver/src/analysis.rs

@@ -266,9 +266,7 @@ pub(crate) fn factor_symmetric(a: &Csr, limits: &Limits, kind: Kind) -> std::res
 /// a singular pivot.
 pub(crate) fn factor_error(e: FactorError, mesh: &Mesh, reduction: &Reduction) -> Error {
     match e {
-        FactorError::TooLarge { entries, limit } => {
-            Error::Limit(format!("the factorization needs {entries} entries; the limit is {limit} (refine less or raise the limit)"))
-        }
+        FactorError::TooLarge { entries, limit } => Error::factor_limit(entries, limit),
         FactorError::OutOfMemory { entries } => Error::Limit(format!("not enough memory for the factorization ({entries} entries)")),
         FactorError::Internal(what) => Error::Internal(what),
         FactorError::Cancelled => Error::Model(fieldcraft_model::Error::Cancelled),
@@ -733,3 +731,20 @@ impl StepResult {
         .map(Location::Point)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn raised_factor_budget_keeps_the_lanczos_vector_limit() {
+        let neq = Limits::MAX_DOFS;
+        for (entries, expected) in [(400_000_000, 33), (2_000_000_000, 166)] {
+            let limits = Limits { max_factor_entries: entries, ..Limits::default() };
+            let vectors = lanczos_basis(&limits, neq);
+            assert_eq!(vectors, expected);
+            assert!(2 * neq * vectors <= entries);
+            assert_eq!(lanczos_basis(&Limits { max_lanczos_vectors: 7, ..limits }, neq), 7);
+        }
+    }
+}