Can I use rnorm_multi to generate data for 3 variables but with only 2 correlations? I'm trying to generate values for 3 variables. Variable A is correlated with B and C, but B and C are not correlated. How should I go about doing this?
At first I tried using rnorm_multi, but I cannot run the code with only 2 correlation values.
And then I tried running rnorm_multi twice, the first was to generate values for A and B, and the second was to generate values for A and C. However, I cannot join the 2 vectors together because of the different values of A.
Is rnorm_multi appropriate in this case or is there another way of doing this?

The uncorrelated variables are correlated with correlation equal to zero. If you input to your function a correlation of zero between $B$ and $C$, I expect your code to run. If the function does not like this, you can use MASS::mvrnorm.
The key from a statistical standpoint, however, is that uncorrelated variables do not have an undefined correlation between them; they have correlation equal to zero.
