why do i keep getting this error?

Solve IVP numerically using forward Euler's method with Nsmall timesteps (use variable names as instructed). [t8,y8]=euler(f,[0,0.8],4,8);[t8(end-4:end),y8(end-9e Incorrect number or types of inputs or outputs for function 'euler'. Solve IVP numerically using forward Euler's method with Nmed timesteps (use variable names as instructed). [t80,y80]=euler(f,[0,0.8],4,80);[t80(end4::end),y80(end