Source Code for Module lib.dispersion.ns_r1rho_2site

  1  ############################################################################### 
  2  #                                                                             # 
  3  # Copyright (C) 2000-2001 Nikolai Skrynnikov                                  # 
  4  # Copyright (C) 2000-2001 Martin Tollinger                                    # 
  5  # Copyright (C) 2013-2014 Edward d'Auvergne                                   # 
  6  #                                                                             # 
  7  # This file is part of the program relax (http://www.nmr-relax.com).          # 
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 20  # along with this program.  If not, see <http://www.gnu.org/licenses/>.       # 
 21  #                                                                             # 
 22  ############################################################################### 
 23   
 24  # Module docstring. 
 25  """The numerical solution for the 2-site Bloch-McConnell equations for R1rho-type data, the U{NS R1rho 2-site<http://wiki.nmr-relax.com/NS_R1rho_2-site>} model. 
 26   
 27  Description 
 28  =========== 
 29   
 30  This is the model of the numerical solution for the 2-site Bloch-McConnell equations.  It originates from the funNumrho.m file from the Skrynikov & Tollinger code (the sim_all.tar file U{https://web.archive.org/web/https://gna.org/support/download.php?file_id=18404} attached to U{https://web.archive.org/web/https://gna.org/task/?7712#comment5}). 
 31   
 32   
 33  References 
 34  ========== 
 35   
 36  The solution has been modified to use the from presented in: 
 37   
 38      - Korzhnev, D. M., Orekhov, V. Y., and Kay, L. E. (2005).  Off-resonance R(1rho) NMR studies of exchange dynamics in proteins with low spin-lock fields:  an application to a Fyn SH3 domain.  I{J. Am. Chem. Soc.}, B{127}, 713-721. (U{DOI: 10.1021/ja0446855<http://dx.doi.org/10.1021/ja0446855>}). 
 39   
 40   
 41  Links 
 42  ===== 
 43   
 44  More information on the NS R1rho 2-site model can be found in the: 
 45   
 46      - U{relax wiki<http://wiki.nmr-relax.com/NS_R1rho_2-site>}, 
 47      - U{relax manual<http://www.nmr-relax.com/manual/NS_2_site_R1_model.html>}, 
 48      - U{relaxation dispersion page of the relax website<http://www.nmr-relax.com/analyses/relaxation_dispersion.html#NS_R1rho_2-site>}. 
 49  """ 
 50   
 51  # Dependency check module. 
 52  import dep_check 
 53   
 54  # Python module imports. 
 55  from math import atan, cos, log, pi, sin, sqrt 
 56  from numpy import dot 
 57   
 58  # relax module imports. 
 59  from lib.dispersion.ns_matrices import rr1rho_3d 
 60  from lib.float import isNaN 
 61  from lib.linear_algebra.matrix_exponential import matrix_exponential 
 62   
 63   
 64 -def ns_r1rho_2site(M0=None, matrix=None, r1rho_prime=None, omega=None, offset=None, r1=0.0, pA=None, pB=None, dw=None, k_AB=None, k_BA=None, spin_lock_fields=None, relax_time=None, inv_relax_time=None, back_calc=None, num_points=None): 
 65      """The 2-site numerical solution to the Bloch-McConnell equation for R1rho data. 
 66   
 67      This function calculates and stores the R1rho values. 
 68   
 69   
 70      @keyword M0:                This is a vector that contains the initial magnetizations corresponding to the A and B state transverse magnetizations. 
 71      @type M0:                   numpy float64, rank-1, 7D array 
 72      @keyword matrix:            A numpy array to be populated to create the evolution matrix. 
 73      @type matrix:               numpy rank-2, 6D float64 array 
 74      @keyword r1rho_prime:       The R1rho_prime parameter value (R1rho with no exchange). 
 75      @type r1rho_prime:          float 
 76      @keyword omega:             The chemical shift for the spin in rad/s. 
 77      @type omega:                float 
 78      @keyword offset:            The spin-lock offsets for the data. 
 79      @type offset:               numpy rank-1 float array 
 80      @keyword r1:                The R1 relaxation rate. 
 81      @type r1:                   float 
 82      @keyword pA:                The population of state A. 
 83      @type pA:                   float 
 84      @keyword pB:                The population of state B. 
 85      @type pB:                   float 
 86      @keyword dw:                The chemical exchange difference between states A and B in rad/s. 
 87      @type dw:                   float 
 88      @keyword k_AB:              The rate of exchange from site A to B (rad/s). 
 89      @type k_AB:                 float 
 90      @keyword k_BA:              The rate of exchange from site B to A (rad/s). 
 91      @type k_BA:                 float 
 92      @keyword spin_lock_fields:  The R1rho spin-lock field strengths (in rad.s^-1). 
 93      @type spin_lock_fields:     numpy rank-1 float array 
 94      @keyword relax_time:        The total relaxation time period for each spin-lock field strength (in seconds). 
 95      @type relax_time:           float 
 96      @keyword inv_relax_time:    The inverse of the relaxation time period for each spin-lock field strength (in inverse seconds).  This is used for faster calculations. 
 97      @type inv_relax_time:       float 
 98      @keyword back_calc:         The array for holding the back calculated R2eff values.  Each element corresponds to one of the CPMG nu1 frequencies. 
 99      @type back_calc:            numpy rank-1 float array 
100      @keyword num_points:        The number of points on the dispersion curve, equal to the length of the tcp and back_calc arguments. 
101      @type num_points:           int 
102      """ 
103   
104      # Repetitive calculations (to speed up calculations). 
105      Wa = omega                  # Larmor frequency [s^-1]. 
106      Wb = omega + dw             # Larmor frequency [s^-1]. 
107      W = pA*Wa + pB*Wb           # Population-averaged Larmor frequency [s^-1]. 
108      dA = Wa - offset            # Offset of spin-lock from A. 
109      dB = Wb - offset            # Offset of spin-lock from B. 
110      d = W - offset              # Offset of spin-lock from population-average. 
111   
112      # Loop over the time points, back calculating the R2eff values. 
113      for i in range(num_points): 
114          # The matrix that contains all the contributions to the evolution, i.e. relaxation, exchange and chemical shift evolution. 
115          rr1rho_3d(matrix=matrix, R1=r1, r1rho_prime=r1rho_prime, pA=pA, pB=pB, wA=dA, wB=dB, w1=spin_lock_fields[i], k_AB=k_AB, k_BA=k_BA) 
116   
117          # The following lines rotate the magnetization previous to spin-lock into the weff frame. 
118          theta = atan(spin_lock_fields[i]/dA) 
119          M0[0] = sin(theta)    # The A state initial X magnetisation. 
120          M0[2] = cos(theta)    # The A state initial Z magnetisation. 
121   
122          # This matrix is a propagator that will evolve the magnetization with the matrix R. 
123          Rexpo = matrix_exponential(matrix*relax_time) 
124   
125          # Magnetization evolution. 
126          MA = dot(M0, dot(Rexpo, M0)) 
127   
128          # The next lines calculate the R1rho using a two-point approximation, i.e. assuming that the decay is mono-exponential. 
129          if MA <= 0.0 or isNaN(MA): 
130              back_calc[i] = 1e99 
131          else: 
132              back_calc[i]= -inv_relax_time * log(MA) 
133