fix eigmin and eigmax sign (#413)

* Remove deprecations; update `norm` behavior

* update docs, misc tweaks

* fix latex

* fix

* allow building docs while skipping examples

* smaller `huber` example

* fix docstring

* do the norm deprecation in 2 steps

* leave for next PR

* fix `eigmin` and `eigmax` sign

Author: ericphanson

NEWS.md

@@ -5,6 +5,7 @@
 * Changes to the `sign` of atoms:
     * The sign of `sumlargesteigs` has been changed from `Positive` to  `NoSign()` instead of `Positive()`, to allow non-positive-semidefinite inputs. This has the potential
   to break code that required that sign to be positive. If you run into this problem, please file an issue so we can figure out a workaround. [#412](https://github.com/jump-dev/Convex.jl/pull/412)
+    * The sign of `eigmin` and `eigmax` has been changed from `Positive` to  `NoSign()`. This is a bugfix because in general `eigmin` and `eigmax` do not need to return a positive quantity (for non-positive-semidefinite inputs). Again, this has the potential to break code that required that sign to be positive. If you run into this problem, please file an issue so we can figure out a workaround. [#412](https://github.com/jump-dev/Convex.jl/pull/413)
 * Removal of deprecations
     * `lambdamin` and `lambdamax` has been deprecated to `eigmin` and `eigmax` since Convex v0.13.0. This deprecation has been removed, so your code must be updated to call `eigmin` or `eigmax` instead. [#412](https://github.com/jump-dev/Convex.jl/pull/412)
     * `norm(x, p)` where `x` is a matrix expression has been deprecated to `opnorm(x,p)` since Convex v0.8.0. This deprecation has been removed, so your code must be updated to call `opnorm(x, p)` instead. Currently, `norm(x,p)` for a matrix

src/atoms/sdp_cone/eig_min_max.jl

@@ -28,7 +28,7 @@ struct EigMaxAtom <: AbstractExpr
 end
 
 function sign(x::EigMaxAtom)
-    return Positive()
+    return NoSign()
 end
 
 function monotonicity(x::EigMaxAtom)
@@ -81,7 +81,7 @@ struct EigMinAtom <: AbstractExpr
 end
 
 function sign(x::EigMinAtom)
-    return Positive()
+    return NoSign()
 end
 
 function monotonicity(x::EigMinAtom)

test/test_utilities.jl

@@ -1,4 +1,5 @@
 using Convex: AbstractExpr, ConicObj
+using LinearAlgebra
 
 # It's not super easy to capture the output
 # I ended up using this pattern from Suppressor: