http://tensorflow.org/tutorials/mnist/beginners/index.md#the_mnist_data
https://upload.wikimedia.org/math/7/3/f/73fc7ef1bf6f6822115c41cff58535e1.png
http://api.tensorflow.org/system/image/body/1704/softmax-regression-scalargraph.png
http://api.tensorflow.org/system/image/body/1707/softmax-regression-scalarequation.png
http://api.tensorflow.org/system/image/body/1705/softmax-regression-vectorequation.png
scalar equation should be:
[W11 * X1 + W12 * X2 + W13 * X3 + b1]
[W21 * X1 +W22 * X2 + W23 * X3 + b2]
[W31 * X1 + W32 * X2 + W33 * X3 + b3]