Apologies for this basic question. I don't have a deep understanding of this function but I was pretty sure it would be zero if logits and label inputs are identical. I found out my MLP model solves my classification problem pretty well but the cost function is never actually 0 (rather it approaches something like -2.14442e+07 but never is actually 0). I have tested what happens if set logits and labels to the same input and still its the same. I use the tensorflow tf.nn.softmax_cross_entropy_with_logits as cost function. Thank you for your help. 
Should softmax cross entropy with logits always be zero if logits and labels are identical?
machine learning;classification;tensorflow