Adding Gurson material model

[TeroFrondelius]

No description provided.

[ahojukka5]

I think we should use Int instead of Int64. This is not a big issue but with 32-bit machines, Int will be Int32 and with 64-bit machines, it will be Int64, automatically. So this way the code will be compatible with all kinds of machines.

julia> Int
Int64

[ahojukka5]

So here, instead of Int64, Int is a better choice.

[TeroFrondelius]

Ok. I will change all. How about Float64, is that ok?

[ahojukka5]

A good question. I think that the use of Float64 is ok. I'm not sure about why this Int32/Int64 is a problem with integers but not with floats. In principle, you could use template to have two structs, one for Float32 and another for Float64, but I have not seen these kinds of practices anywhere so far. So I think that Int and Float64 is the right way to go.

https://docs.julialang.org/en/v1/manual/integers-and-floating-point-numbers/

[ahojukka5]

And this is only when defining structs. When defining new functions, the use of abstract types is not hitting performance at all.

function foo(x::AbstractFloat, y::Integer)
    # do something with `x` and `y`
end

is perfectly fine.

[TeroFrondelius]

@ahojukka5 any ideas, where my problem is? When I run the test UMAT first time, I usually get this error:

** On entry to DGESV   parameter number  4 had an illegal value

But it will go away if I run test UMAT a few times and the test passes. In Travis, Linux build, it seems to fail systematically. I think I have a problem with setting the model correctly.

[ahojukka5]

It has something to do with matrix dimensions?

[TeroFrondelius]

It has something to do with matrix dimensions?

I hope #11 will fix the problem. See issue #10.