error: operator -: nonconformant arguments (op1 is 3x1, op2 is 10x1)

[ishi soichi]

my code generates an error

error: operator -: nonconformant arguments (op1 is 3x1, op2 is 10x1)

error:   /Users/xxx at line 133, column 9

which is at 

delta_3 = a_3 - yy;

delta_3 is newly defined variable. 

if I put,

size(a_3)

size(yy)

it certainly, 

ans =

   10    1

ans =

   10    1

so, the nonconformat error does not make sense at all.

If I remove either "a_3" or "yy", the error does not appear although the output is wrong.

Is there any other possibility of making such errors?

soichi