# Bayesian inference with multiple forward model with different numbers of provided measurements but with one common discrepancy model and parameter?

**URL:** <https://uqworld.org/t/bayesian-inference-with-multiple-forward-model-with-different-numbers-of-provided-measurements-but-with-one-common-discrepancy-model-and-parameter/621>\
**Category:** Community Q&A and How To\
**Tags:** inversion\
**Created:** [May 29, 2020, 3:47pm UTC](https://uqworld.org/t/bayesian-inference-with-multiple-forward-model-with-different-numbers-of-provided-measurements-but-with-one-common-discrepancy-model-and-parameter/621 "2020-05-29T15:47:22Z")\
**Posts on this page:** 1\
**Showing post:** 17

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**Author:** ![olaf.klein](https://uqworld.org/user_avatar/uqworld.org/olaf.klein/32/468_2.png) [@olaf.klein](https://uqworld.org/u/olaf.klein)\
**Post date:** [June 30, 2020, 12:50pm UTC](https://uqworld.org/t/bayesian-inference-with-multiple-forward-model-with-different-numbers-of-provided-measurements-but-with-one-common-discrepancy-model-and-parameter/621/17 "2020-06-30T12:50:38Z")

</div>

Dear Paul-Remo,

I think I found again a hidden error.

After increasing the number of `Solver.MCMC.NChains` to 500 and the number of `Solver.MCMC.Step` to 600 and performing Bayesian Inference for a model with 29 output components by calling `myBayesianAnalysis = uq_createAnalysis(BayesOpts)`, I got an error message during the creation of the scatter plot during the evaluation of `uq_display(myBayesianAnalysis)` (see below).

Using the debugger, I figured out that the problem seems to be the line 278 in your new version of `uq_display_uq_inversion.m`:

```
PlotId = round(rand(NMaxPlot,1)*size(scatterplotPost_Sample,1));

```

which is only evaluated if `1E5= NMaxPlot < size(scatterplotPost_Sample,1)`,  
which is not the case in the typical examples. The following call of `scatterplotPost_Sample(PlotId,scatterplotParams);`  
in the line 282 afterwards generates the error message

```
Subscript indices must either be real positive integers or logicals.

Error in uq_display_uq_inversion (line 282)
PostSample = scatterplotPost_Sample(PlotId,scatterplotParams);

Error in uq_module/Display

Error in uq_display (line 4)
% uq_createModel, uq_createInput or uq_createAnalysis commands. The

Error in Scr_extr_UQLab_1st_dec_2a (line 106)
uq_display(myBayesianAnalysis)

```

…

It seem to me that `scatterplotPost_Sample` has problems since in general some components in `PlotId` defined according to the above equation will coincide. Moreover, in some situations at lest one component of `PlotId` may be equal to 0, which also creates problems when calling `scatterplotPost_Sample`. Replacing the above code in the line 278 by

```
   PlotId = 1+unique( round(rand(NMaxPlot,1)*...
                     (size(scatterplotPost_Sample,1)-1)));

```

I could not observe any error message during several further evaluation of  
`uq_display(myBayesianAnalysis)` using `myBayesianAnalysis` with the same the same contents as above.

One further remark, I would be grateful if it would be pointed out in the manual, e.g. in the discussion of the parameters for `uq_display`, that the _mean prediction_ shown in the data group plot is **not** the mean of the ``posterior predective’’ density also shown in these plot, but the model output at the mean of the samples for the model parameters. For nonlinear models these two values can be quite different, especially if one is considering results of `uq_createAnalysis` performed with using too few steps the MCMC-solver, as in my intermediate result:

![more_MCMC_steps-needed](https://uqworld.org/uploads/default/original/1X/1643dd4f233cdb75caf3228b7d6f2e3b031cf5f4.png)

Greetings  
Olaf

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