[SOFIE] Add regression test for ELU with alpha != 1.0

Adds EluAlpha.onnx (alpha=0.5) and a corresponding test case to
prevent regressions for non-default alpha values in ELU codegen.

Refs #21539

Author: Neeraj-x0

tmva/sofie/test/TestCustomModelsFromONNX.cxx

@@ -92,6 +92,7 @@ constexpr auto modelDataSuffix = "_FromONNX.dat";
 #include "input_models/references/Log.ref.hxx"
 #include "input_models/references/Elu.ref.hxx"
 #include "input_models/references/Equal.ref.hxx"
+#include "input_models/references/EluAlpha.ref.hxx"
 #include "input_models/references/LessOrEqual.ref.hxx"
 #include "input_models/references/GreaterOrEqual.ref.hxx"
 #include "input_models/references/Less.ref.hxx"
@@ -308,6 +309,22 @@ TEST(ONNX, Elu)
          EXPECT_LE(std::abs(output[i] - correct[i]), TOLERANCE);
       }
    }
+TEST(ONNX, EluAlpha)
+   {
+      constexpr float TOLERANCE = DEFAULT_TOLERANCE;
+      // Regression test for alpha != 1.0 (fixes #21539)
+      std::vector<float> input({
+        1.0, -2.0, 3.0, 0.5, -1.0, 2.0
+      });
+      ASSERT_INCLUDE_AND_RUN(std::vector<float>, "EluAlpha", input);
+      // Checking output size
+      EXPECT_EQ(output.size(), sizeof(EluAlpha_ExpectedOutput::outputs) / sizeof(float));
+      float *correct = EluAlpha_ExpectedOutput::outputs;
+      // Checking every output value, one by one
+      for (size_t i = 0; i < output.size(); ++i) {
+         EXPECT_LE(std::abs(output[i] - correct[i]), TOLERANCE);
+      }
+   }
 
 TEST(ONNX, Constant)
 {

tmva/sofie/test/input_models/EluAlpha.onnx

@@ -0,0 +1,6 @@
+namespace EluAlpha_ExpectedOutput{
+	float outputs[] = {
+     1.0000, -0.4323,  3.0000,
+     0.5000, -0.3161,  2.0000
+	};
+} // namespace EluAlpha_ExpectedOutput