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THE BAYES ANALYZE ERROR MESSAGES
195
36. TRANS – Program Error Contact Varian
37. ALOGP – Possible Program Error Investigate Further
38. ALOGP2 – Possible Program Error Investigate Further
39. SETMODEL – Program Error Contact Varian
40. SCCETRANS – Program Error Contact Varian
41. SCUETRANS – Program Error Contact Varian
42. GETMODEL – Program Error Contact Varian
43. APPEND TEXT – Program Error Contact Varian
44. READHDR – Program Error Contact Varian
45. WRITEDATA – Program Error Contact Varian
46. WRITEMODEL – Program Error Contact Varian
47. WRITERESID – Program Error Contact Varian
48. COPY PROCPAR – Program Error Contact Varian
49. LIST MODEL – Program Error Contact Varian
The two exceptions that we were discussing are messages numbers 37 and 38. These two messages
are program errors, but they may be caused by the model. For example if the estimated frequencies
become redundant, then the covariance matrix will be singular and these errors are issued. Message
number 37 indicates that this matrix is singular. When this matrix becomes singular it is almost
always because one or more of the resonances have converged to the same resonance frequency. This
behavior may occur under several circumstances: first it is possible that a peak was marked and
this peak was so far from the value indicated by probability theory that Bayes Analyze added one
or more additional resonances near the same location. These resonances are nearly identical and
this can cause the error. The easiest thing to try under these conditions is to remove the offending
resonances and allow Bayes Analyze to run in its automatic model. There is one other condition
where this problem has been known to occur. NMR lines never decay in a perfectly exponential
manner because the magnetic fields are never perfectly uniform. When the signal-to-noise is very
very high Bayes Analyze may try to fit so many resonances at nearly the same resonance frequency
that the matrix it is trying to invert becomes singular. Unfortunately, in this case, there is very
little that can be done. You can try turning on the shimming models and rerunning the analysis,
but if the problem re-occurs then you may not be able to analyze this data.
So far we have been discussing error number 37, but error number 38 is almost the same and it
is caused by essentially the same conditions. The previous error occurs when the matrix inversion
routine detects that the matrix is singular. Here the inversion routine did not detect failure and it
returned a zero status. After the inverse is computed, Bayes Analyze computes the projection of
the data onto the model. What it found was that the projection of the data onto the model was
greater than the projection of the data onto itself. This is simply not possible, and when it happens
it means that the matrix inverse failed.