The InputDelay must either be a scalar for a SISO system or a Nu-by-1 vector for multi-input system, where the numerator, denominator is specified as an Ny-by-Nu cell array of row vectors to specify a MIMO transfer function, where Ny is the number of outputs and Nu is the number of inputs.
In this case the value of Ny = 7 and Nu = 1. Hence the size of 'InputDelay' vector cannot can be 7x1.
Refer to the documentation of tf and description of numerator, denominator & InputDelay for more information.
