computeGradients(f, varList) {
        return (0, _gradients.variableGrads)(f, varList);
    }
Executes f() and computes the gradient of the scalar output of f() with
respect to the list of trainable variables provided by `varList`. If no
list is provided, it defaults to all trainable variables.

@param f The function to execute and whose output to use for computing
gradients with respect to variables.
@param varList An optional list of variables to compute gradients with
respect to. If specified, only the trainable variables in varList will have
gradients computed with respect to. Defaults to all trainable variables.

@doc {heading: 'Training', subheading: 'Optimizers'}