We are pleased to announce the release of Chebfun Version 5.1 for numerical computing with 1D and 2D functions. The main new features are:

• Fast solution of ODE initial-value problems via "\" (see Chebfun Guide, Chapter 10)
• Updated CHEBGUI interface for ODE, PDE, and eigenvalues
• New "trig" capabilities for periodic functions and ODEs (see Chebfun Guide, Chapter 11)
• New function collections gallery, gallerytrig, gallery2 (see Chebfun Guide, Section 1.8)

Also note these new developments:

• Rewritten Chapter 10 of the Chebfun Guide discusses ODE IVPs
• New Chapter 11 of the Chebfun Guide for periodic functions
• Chebfun now has an active wiki on its GitHub page
• Chebfun User's Day will take place on 17 March at Oxford

There are a number of new Examples in the collection which demonstrate the use of new features. Among them are the following:

• Galleries: Gallery and Gallerytrig
• IVPs: Pythagorean planets · Modelling infectious disease outbreaks
• Periodic functions: Fourier spectral collocation · Nonlinear periodic ODE · A periodic ODE system · Time-dependent PDEs on a periodic interval with EXPM · Periodic ODE eigenvalue problems