Spark ml.ALS question -- RegressionEvaluator .evaluate giving ~1.5 output for same train and predict data

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I am trying to run ml.ALS to compute some recommendations.

Just to test I am using the same dataset for training using ALSModel and
for predicting the results based on the model .

When I evaluate the result using RegressionEvaluator I get a
Root-mean-square error = 1.5544064263236066

I thin this should be 0. Any suggestions what might be going wrong.

Regards,
Vipul