The purpose of this tutorial is to calculate the exponent of the isotropic spin-1/2 Heisenberg model using transfer matrix techniques.

The starting point is the wavefunction we obtained previously, using the `xxx`

or `xxx-u1`

models. But now we will want to constuct a series of wavefunctions for successively larger number of states kept, for example m=10, 20, 30, 40, 50. Firstly, use mp-icorrelation to construct and plot the spin-spin correlation function for each of these wavefunctions.

The tool for constructing the transfer matrix spectrum is `mp-ispectrum`

. We can use this to calculate both the correlation length \xi and the prefactor *a* in the transfer matrix expansion of the correlator. Plot the prefactor versus the correlation length for each value of m and verify that the exponent is close to the known value of 1.