> Yeah you're right, the subdifferential of f(x)=|x| at the origin is the interval [−1, 1]. I'm confused where you're seeing absolute value? I never had absolu

> Yeah you're right, the subdifferential of f(x)=|x| at the origin is the interval [−1, 1]. I'm confused where you're seeing absolute value? I never had absolute value anywhere. The second example I wrote just amounted to y = x.