The following error occurred converting from sym to double: Unable to convert expression into double array.

The following error occurred converting from sym to double:

Unable to convert expression into double array. main purpose is to create a matrix which has unknowns x and y which will be calculated later. So I already created ONM matrix( size 4x1)

After that I tried to assign the elements of ONM matrix to 3rd column of another matrix that is called NM (size 4x1). But the error occured.

How can I fix it?

Thanks for your help

syms x y real
ONM1=[0 x y 0]
ONM=ONM1'
NM(:,3)=(ONM(:,2))

[Gülçin Tekin Özkan]

Thank you so much for your kind and explicative answer. It works.

Answer 1

[Walter Roberson]

When you created NM, you created it as a numeric array. You cannot "upgrade" a numeric array to be symbolic by assigning symbolic elements in the middle of it.

Before doing that last assignment, do

NM = sym(NM);

or arrange for NM to be constructed as sym when it is created.