# Discussion Forum

## "Constant" choice in Element Order for Discontinuous Lagrange Shape Function!

Hi. I'm using COMSOL PDE to solve a set of partial differential equations that are linked together. In element order, there is a "constant" choice, but I don't know what that means! For example, I know what a "linear" element order means, but I don't know what a "constant" option means here. I get a better result with that choice! This "constant" choice only shows up in element order when the "Discontinuous Lagrange" shape function is chosen. So, what does that mean compared to "Linear," "Quadratic," and other choices? Thank you in advance for your help. Best, Mahdi

3 Replies Last Post May 25, 2023, 2:18 p.m. EDT

Posted: 2 weeks ago

The value of the field described by this shape function is constant over each element. One effect is that it cannot be differentiated, since its gradient is zero.

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Henrik Sönnerlind
COMSOL

Posted: 2 weeks ago
Updated: 2 weeks ago

Thank you.

Posted: 2 weeks ago

The value of the field described by this shape function is constant over each element. One effect is that it cannot be differentiated, since its gradient is zero.

Hi Henrik. Thanks for the explanation.

It is a surface evolution model, and z coordinate is the field to be solved with respect to time and (x,y) coordinates. After some run time, the geometry is still curved; it was initially an intact sphere and it is now a deformed sphere. How a smooth curved shape is possible using a constant shape function? Can you explain this more?

And, does constant shape function have the ability to capture the numerical solution accurately?