Page 85 - A Guide to MATLAB for Beginners and Experienced Users

66 Chapter 4: Beyond the Basics

solve(’x+y=3’) solves for x, not y. If you want to solve for y in this
example, you need to enter solve(’x+y=3’, ’y’). MATLAB’s default
variable for solve is x. If there is no x in the equation(s), MATLAB looks for
the letter nearest to x in alphabetical order (where y takes precedence over w,
but w takes precedence over z, etc). Similarly for diff, int, and many other
symbolic commands. Thus syms w z; diff w*z yields z as an answer. On
occasion MATLAB assigns a different primary default variable — for example,
the default independent variable for MATLAB’s symbolic ODE solver dsolve
is t. This is mentioned clearly in the online help for dsolve. If you have doubt
about the default variables for any MATLAB command, you should check the
online help.