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diff --git a/src/main/java/org/apache/commons/math3/ode/events/Transformer.java b/src/main/java/org/apache/commons/math3/ode/events/Transformer.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.math3.ode.events;
+
+import org.apache.commons.math3.util.FastMath;
+import org.apache.commons.math3.util.Precision;
+
+
+/** Transformer for {@link EventHandler#g(double, double[]) g functions}.
+ * @see EventFilter
+ * @see FilterType
+ * @since 3.2
+ */
+enum Transformer {
+
+    /** Transformer computing transformed = 0.
+     * <p>
+     * This transformer is used when we initialize the filter, until we get at
+     * least one non-zero value to select the proper transformer.
+     * </p>
+     */
+    UNINITIALIZED {
+        /**  {@inheritDoc} */
+        @Override
+        protected double transformed(final double g) {
+            return 0;
+        }
+    },
+
+    /** Transformer computing transformed = g.
+     * <p>
+     * When this transformer is applied, the roots of the original function
+     * are preserved, with the same {@code increasing/decreasing} status.
+     * </p>
+     */
+    PLUS {
+        /**  {@inheritDoc} */
+        @Override
+        protected double transformed(final double g) {
+            return g;
+        }
+    },
+
+    /** Transformer computing transformed = -g.
+     * <p>
+     * When this transformer is applied, the roots of the original function
+     * are preserved, with reversed {@code increasing/decreasing} status.
+     * </p>
+     */
+    MINUS {
+        /**  {@inheritDoc} */
+        @Override
+        protected double transformed(final double g) {
+            return -g;
+        }
+    },
+
+    /** Transformer computing transformed = min(-{@link Precision#SAFE_MIN}, -g, +g).
+     * <p>
+     * When this transformer is applied, the transformed function is
+     * guaranteed to be always strictly negative (i.e. there are no roots).
+     * </p>
+     */
+    MIN {
+        /**  {@inheritDoc} */
+        @Override
+        protected double transformed(final double g) {
+            return FastMath.min(-Precision.SAFE_MIN, FastMath.min(-g, +g));
+        }
+    },
+
+    /** Transformer computing transformed = max(+{@link Precision#SAFE_MIN}, -g, +g).
+     * <p>
+     * When this transformer is applied, the transformed function is
+     * guaranteed to be always strictly positive (i.e. there are no roots).
+     * </p>
+     */
+    MAX {
+        /**  {@inheritDoc} */
+        @Override
+        protected double transformed(final double g) {
+            return FastMath.max(+Precision.SAFE_MIN, FastMath.max(-g, +g));
+        }
+    };
+
+    /** Transform value of function g.
+     * @param g raw value of function g
+     * @return transformed value of function g
+     */
+    protected abstract double transformed(double g);
+
+}