Hi, I am trying to model a simple 1DOF suspension system [mass(ms) 300kg, stiffness(k) 15000N/m, damping coefficient(c) 2500Ns/m. Its subjected to different inputs and then needs to simulate the dynamic response of the system to a road surface that has the characteristics of a flat road, a sine wave surface and then a step. I completed the model. However, i have now opened the file again and i keep getting the error message: Error evaluating parameter 'Numerator' in 'HC1/Transfer Fcn': Undefined function or variable 'c' I have defined "c" as 2500 in the "m" file and the matlab working directory is correct as far as i know. I have attached a screen shot of the error. Does any1 know how to solve this problem?