# Degree modification of multivariate polynomial chaos surrogate model

**URL:** <https://discourse.julialang.org/t/degree-modification-of-multivariate-polynomial-chaos-surrogate-model/84145>\
**Category:** Modelling & Simulations\
**Tags:** question\
**Created:** [July 13, 2022, 5:35am UTC](https://discourse.julialang.org/t/degree-modification-of-multivariate-polynomial-chaos-surrogate-model/84145 "2022-07-13T05:35:06Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![chenr86](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chenr86/32/36785_2.png) [@chenr86](https://discourse.julialang.org/u/chenr86)\
**Post date:** [July 13, 2022, 5:35am UTC](https://discourse.julialang.org/t/degree-modification-of-multivariate-polynomial-chaos-surrogate-model/84145/1 "2022-07-13T05:35:06Z")

</div>

Hello,

I am using `Surrogate.jl` to build my polynomial choas surrogate model. The model is multivariate, with 4 input parameters, and 1D output. I want to change the parameter `op = SurrogatesPolyChaos.GaussOrthoPoly(5)` of the model, but I got an error message. What’s the suitable form for multivariate polynomial chaos model?

```julia
using Surrogates
using SurrogatesPolyChaos
using Plots
default()
function f(x)
    t = x[1]
    w = x[2]
    L = 100.0
    E = 2.770674127819261e7
    X = 530.8038576066307
    Y = 997.8714938733949
    return (4*L^3)/(E*w*t)*sqrt( (Y/t^2)^2 + (X/w^2)^2)
end

n = 100
lb = [1.0,1.0]
ub = [8.0,8.0]
xys = sample(n,lb,ub,SobolSample());
zs = f.(xys);
x, y = 0:8, 0:8
p1 = surface(x, y, (x1,x2) -> f((x1,x2)))
xs = [xy[1] for xy in xys]
ys = [xy[2] for xy in xys]
p2 = contour(x, y, (x1,x2) -> f((x1,x2)))
scatter!(xs, ys)
plot(p1, p2, title="True function")

mypoly = PolynomialChaosSurrogate(xys, zs, lb, ub, op = SurrogatesPolyChaos.GaussOrthoPoly(5))

```

```julia
TypeError: in keyword argument op, expected PolyChaos.MultiOrthoPoly, got a value of type PolyChaos.GaussOrthoPoly{Vector{Float64}, PolyChaos.GaussMeasure, PolyChaos.Quad{Float64, Vector{Float64}}}

```

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<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [July 13, 2022, 8:42am UTC](https://discourse.julialang.org/t/degree-modification-of-multivariate-polynomial-chaos-surrogate-model/84145/2 "2022-07-13T08:42:41Z")

</div>

Can you open an issue?

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<div class="post-metadata">

**Author:** ![chenr86](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chenr86/32/36785_2.png) [@chenr86](https://discourse.julialang.org/u/chenr86)\
**Post date:** [July 13, 2022, 9:00am UTC](https://discourse.julialang.org/t/degree-modification-of-multivariate-polynomial-chaos-surrogate-model/84145/3 "2022-07-13T09:00:22Z")

</div>

I have opened a new issue in github [Degree modification of multivariate polynomial chaos surrogate model · Issue #378 · SciML/Surrogates.jl · GitHub](https://github.com/SciML/Surrogates.jl/issues/378)