Unexpected behaviour in C# when negation operator is used in the very first term

[ohkangkwon]

Running the following C# code:

var fgrad = AD.Grad(v => -v[0] - v[1] * 2.0);
var fgradValue = fgrad(new DV(new double[] {1, 1}));

gives the unexpected result (0, -2.0) [first value should be -1.0]
The result is the same when the first line is modified to:

var fgrad = AD.Grad(v => -v[0] * 5.0 - v[1] * 2.0); // still gives (0, -2.0) at (1, 1)

The correct result is given when the code is changed to:

var fgrad = AD.Grad(v => -1.0 * v[0] - v[1] * 2.0); // and
var fgrad = AD.Grad(v => -5.0 * v[0] - v[1] * 2.0);

DiffSharp version: 0.7.7.0

[dsyme]

I checked in dev and the result is correct

open DiffSharp

let fgrad = dsharp.grad(fun v -> -v.[0] - v.[1] * 2.0);
let fgradValue = fgrad(dsharp.tensor [ 1.0, 1.0 ])

printfn "fgradValue = %A" fgradValue

gives

fgradValue = Tensor [-1.000000, -2.000000]

I'll close this out for this reason - see README for building dev branch