# In FEM, what are the elements in which the same shape functions describe the geometry and field displacement variables?

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In FEM, what are the elements in which the same shape functions describe the geometry and field displacement variables?

(a) Iso-parametric

(b) Axi-Symmetric

(c) Super-parametric

(d) Sub-parametric

I got this question in final exam.

My query is from Library of Elements and Interpolation Functions topic in section Interpolation Functions, Numerical Integration and Modelling Considerations of Finite Element Method

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The correct option is (a) Iso-parametric

For explanation: In sub-parametric formulations, the geometry is represented by elements of a lower order than those used to approximate the dependent variable. An example of this category is provided by the beam element. In iso-parametric formulations (which are the most common in practice), the same element is used to approximate the geometry as well as the dependent unknowns. In super-parametric formulations, the geometry is represented by elements of a higher order than those used to approximate the dependent variables.

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