Add lbfgs_strerror().

include/lbfgs.h

@@ -515,6 +515,13 @@ lbfgsfloatval_t* lbfgs_malloc(int n);
  */
 void lbfgs_free(lbfgsfloatval_t *x);
 
+/**
+ * Get string description of an lbfgs() return code.
+ *
+ *  @param err          A value returned by lbfgs().
+ */
+const char* lbfgs_strerror(int err);
+
 /** @} */
 
 #ifdef  __cplusplus

lib/lbfgs.c

@@ -640,6 +640,119 @@ lbfgs_exit:
     return ret;
 }
 
+const char* lbfgs_strerror(int err)
+{
+    switch(err) {
+        case LBFGS_SUCCESS:
+            /* Also handles LBFGS_CONVERGENCE. */
+            return "Success: reached convergence (gtol).";
+
+        case LBFGS_STOP:
+            return "Success: met stopping criteria (ftol).";
+
+        case LBFGS_ALREADY_MINIMIZED:
+            return "The initial variables already minimize the objective function.";
+
+        case LBFGSERR_UNKNOWNERROR:
+            return "Unknown error.";
+
+        case LBFGSERR_LOGICERROR:
+            return "Logic error.";
+
+        case LBFGSERR_OUTOFMEMORY:
+            return "Insufficient memory.";
+
+        case LBFGSERR_CANCELED:
+            return "The minimization process has been canceled.";
+
+        case LBFGSERR_INVALID_N:
+            return "Invalid number of variables specified.";
+
+        case LBFGSERR_INVALID_N_SSE:
+            return "Invalid number of variables (for SSE) specified.";
+
+        case LBFGSERR_INVALID_X_SSE:
+            return "The array x must be aligned to 16 (for SSE).";
+
+        case LBFGSERR_INVALID_EPSILON:
+            return "Invalid parameter lbfgs_parameter_t::epsilon specified.";
+
+        case LBFGSERR_INVALID_TESTPERIOD:
+            return "Invalid parameter lbfgs_parameter_t::past specified.";
+
+        case LBFGSERR_INVALID_DELTA:
+            return "Invalid parameter lbfgs_parameter_t::delta specified.";
+
+        case LBFGSERR_INVALID_LINESEARCH:
+            return "Invalid parameter lbfgs_parameter_t::linesearch specified.";
+
+        case LBFGSERR_INVALID_MINSTEP:
+            return "Invalid parameter lbfgs_parameter_t::max_step specified.";
+
+        case LBFGSERR_INVALID_MAXSTEP:
+            return "Invalid parameter lbfgs_parameter_t::max_step specified.";
+
+        case LBFGSERR_INVALID_FTOL:
+            return "Invalid parameter lbfgs_parameter_t::ftol specified.";
+
+        case LBFGSERR_INVALID_WOLFE:
+            return "Invalid parameter lbfgs_parameter_t::wolfe specified.";
+
+        case LBFGSERR_INVALID_GTOL:
+            return "Invalid parameter lbfgs_parameter_t::gtol specified.";
+
+        case LBFGSERR_INVALID_XTOL:
+            return "Invalid parameter lbfgs_parameter_t::xtol specified.";
+
+        case LBFGSERR_INVALID_MAXLINESEARCH:
+            return "Invalid parameter lbfgs_parameter_t::max_linesearch specified.";
+
+        case LBFGSERR_INVALID_ORTHANTWISE:
+            return "Invalid parameter lbfgs_parameter_t::orthantwise_c specified.";
+
+        case LBFGSERR_INVALID_ORTHANTWISE_START:
+            return "Invalid parameter lbfgs_parameter_t::orthantwise_start specified.";
+
+        case LBFGSERR_INVALID_ORTHANTWISE_END:
+            return "Invalid parameter lbfgs_parameter_t::orthantwise_end specified.";
+
+        case LBFGSERR_OUTOFINTERVAL:
+            return "The line-search step went out of the interval of uncertainty.";
+
+        case LBFGSERR_INCORRECT_TMINMAX:
+            return "A logic error occurred; alternatively, the interval of uncertainty"
+                   " became too small.";
+
+        case LBFGSERR_ROUNDING_ERROR:
+            return "A rounding error occurred; alternatively, no line-search step"
+                   " satisfies the sufficient decrease and curvature conditions.";
+
+        case LBFGSERR_MINIMUMSTEP:
+            return "The line-search step became smaller than lbfgs_parameter_t::min_step.";
+
+        case LBFGSERR_MAXIMUMSTEP:
+            return "The line-search step became larger than lbfgs_parameter_t::max_step.";
+
+        case LBFGSERR_MAXIMUMLINESEARCH:
+            return "The line-search routine reaches the maximum number of evaluations.";
+
+        case LBFGSERR_MAXIMUMITERATION:
+            return "The algorithm routine reaches the maximum number of iterations.";
+
+        case LBFGSERR_WIDTHTOOSMALL:
+            return "Relative width of the interval of uncertainty is at most"
+                   " lbfgs_parameter_t::xtol.";
+
+        case LBFGSERR_INVALIDPARAMETERS:
+            return "A logic error (negative line-search step) occurred.";
+
+        case LBFGSERR_INCREASEGRADIENT:
+            return "The current search direction increases the objective function value.";
+
+        default:
+            return "(unknown)";
+    }
+}
 
 
 static int line_search_backtracking(