Dear all,

I have got a question regarding the specification of observation equations.

My model at hand has a period length of a quarter. I entered my model equations non-linearly into the model-block. However, for all endogenous variables in levels, I used the exp()-substitution in the model-block. I did not use the exp()-substitution for net interest rates and all other variables measured in percentage.

I gathered the time series below:

i) GDP at current prices (quarterly)

ii) GDP deflator (quarterly)

iii) Employment and Unemployment (quarterly, in levels)

iv) HICP index (quarterly)

v) Debt to GDP ratio (quarterly)

vi) Gross fixed capital formation (quarterly)

vii) Euribor1W (quarterly)

Data preparation:

i) Target: **Percentage deviations of GDP from itâ€™s trend**

To obtain a time series of real GDP, I divided the nominal GDP values by the GDP deflator values. Afterwards, I divided real GDP by the active labor force (employment + unemployment) to obtain real GDP per capita. Afterwards, I applied the logarithm and used a log-quadratic trend to extract the cyclical component as percentage deviations from trend. Finally, I demeaned the data series.

ii) Target: **Gross fixed capital formation as a percentage of GDP**

I divided the gross fixed capital formation values by (employment + unemployment). Afterwards, I divided the resulting values by real GDP per capita to obtain gross fixed capital formation as a percentage of real GDP per capita.

iii) Target: **Net inflation rate**

First, I applied the logarithm to HICP index. Then, I calculated log(HICP_{t}) - log(HICP_{t-1}) to obtain values for the net inflation rate.

iv) Target: **Quarterly net interest rate**

I used the Euribor1W to calculate the quarterly net interest rate by

i_{quart} = (1+Euribor1W)^{1/4} - 1

v) Target: **Debt to GDP ratio**

I did not manipulate the gathered data series for the debt to GDP ratio.

Next, I specified the following five observation equations:

// observation equations

percentageDeviationOutput_obs = Y_tilde - steady_state(Y_tilde) + sig_y * eps_y;

i_obs = i;

inflation_obs = pii;

debtGDPRatio_obs = 1/4 * (exp(B_tilde)/exp(Y_tilde));

GFCFAsPercentageOfGDP_obs = (exp(K_tilde)-exp(K_tilde(-1)))/exp(Y_tilde);

where:

pii denotes the net inflation rate.

B is the stock of government debt.

When I use the first two observation equations (DY_obs and i_obs), the estimation works. However, when I include all of them, I get the following error message:

â€žPOSTERIOR KERNEL OPTIMIZATION PROBLEM!

(minus) the hessian matrix at the â€śmodeâ€ť is not positive definite!

=> posterior variance of the estimated parameters are not positive.â€ś

I also tried another optimization routine (â€žmode_compute = 6â€ś and â€žmode_compute = 9â€ś), which unfortunately did not solve the issue. Therefore, I presume that Iâ€™ve most likely misspecified my observation equations.

Could someone give me a hint where I have done something wrong?

Thank you!

Best,

Matthias