test new sampling method

Project/Assets/ML-Agents/Examples/3DBall/Scripts/Ball3DAgent.cs

     public GameObject ball;
     Rigidbody m_BallRb;
     EnvironmentParameters m_ResetParams;
+    float m_MinMass;
+    float m_MaxMass;
+    float m_MinScale;
+    float m_MaxScale;
+
+        m_MinMass = m_ResetParams.GetWithDefault("min_mass", -1.0f);
+        m_MaxMass = m_ResetParams.GetWithDefault("max_mass", -1.0f);
+        m_MinScale = m_ResetParams.GetWithDefault("min_scale", -1.0f);
+        m_MaxScale = m_ResetParams.GetWithDefault("max_scale", -1.0f);
         SetResetParameters();
     }
 
     public void SetBall()
     {
         //Set the attributes of the ball by fetching the information from the academy
-        m_BallRb.mass = m_ResetParams.GetWithDefault("mass", 1.0f);
-        var scale = m_ResetParams.GetWithDefault("scale", 1.0f);
+        var scale = 0f;
+        if (m_MinMass > 0f)
+        {
+            m_BallRb.mass = Random.Range(m_MinMass, m_MaxMass);
+            scale = Random.Range(m_MinScale, m_MaxScale);
+        }
+        else
+        {
+            m_BallRb.mass = m_ResetParams.GetWithDefault("mass", 1.0f);
+            scale = m_ResetParams.GetWithDefault("scale", 1.0f);
+        }
         ball.transform.localScale = new Vector3(scale, scale, scale);
     }
 

config/ppo/3DBall_randomize_exp.yaml

+behaviors:
+  3DBall:
+    trainer_type: ppo
+    hyperparameters:
+      batch_size: 64
+      buffer_size: 12000
+      learning_rate: 0.0003
+      beta: 0.001
+      epsilon: 0.2
+      lambd: 0.99
+      num_epoch: 3
+      learning_rate_schedule: linear
+    network_settings:
+      normalize: true
+      hidden_units: 128
+      num_layers: 2
+      vis_encode_type: simple
+    reward_signals:
+      extrinsic:
+        gamma: 0.99
+        strength: 1.0
+    output_path: default
+    keep_checkpoints: 5
+    max_steps: 500000
+    time_horizon: 1000
+    summary_freq: 12000
+    threaded: true
+
+parameter_randomization:
+  resampling-interval: 5000000
+  min_mass:
+    sampler-type: uniform
+    min_value: 0.5
+    max_value: 0.5
+  max_mass:
+    sampler-type: uniform
+    min_value: 10
+    max_value: 10
+  min_scale:
+    sampler-type: uniform
+    min_value: 0.75
+    max_value: 0.75
+  max_scale:
+    sampler-type: uniform
+    min_value: 3
+    max_value: 3
+  gravity:
+    sampler-type: uniform
+    min_value: 7
+    max_value: 12