Just wrap the scalar expressions in an `as_vector`.

x = SpatialCoordinate(V.mesh())
f.interpolate(as_vector(
   cos(2*pi*x[0])*cos(2*pi*x[1])*cos(2*pi*x[2]),
   cos(2*pi*x[0])*cos(2*pi*x[1])*cos(2*pi*x[2]),
   cos(2*pi*x[0])*cos(2*pi*x[1])*cos(2*pi*x[2])
))

From: firedrake-bounces@imperial.ac.uk <firedrake-bounces@imperial.ac.uk> on behalf of Alexei Colin <acolin@isi.edu>
Date: Monday, 5 April 2021 at 17:48
To: firedrake <firedrake@imperial.ac.uk>
Subject: [firedrake] How to convert tuple of C string expressions to UFL?

Hi, firedrake-bench/elasticity (from 'experiments' branch)
uses C string expressions which are no longer supported.

I read some tips for conversion here, however, the help doesn't cover
the case where there is a tuple of C string expressions:
https://www.firedrakeproject.org/interpolation.html#c-string-expressions

How to convert this?

    f = Function(V)
    f.interpolate(Expression(
         ("cos(2*pi*x[0])*cos(2*pi*x[1])*cos(2*pi*x[2])",
         "cos(2*pi*x[0])*cos(2*pi*x[1])*cos(2*pi*x[2])",
         "cos(2*pi*x[0])*cos(2*pi*x[1])*cos(2*pi*x[2])")))

Please forgive if this is obvious, I have no knowledge in this domain at
all, just trying to blindly run this code. Thank you.

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