**4. The selection of the most representative data vectors for the decision "operate"**

We have already mentioned that we need the "operate" types of patient data vectors as the entries of the NS discrimination algorithm. We thus want to prepare typical data strings for the decision "operate" in advance.

Let us first treat the vector *v* = (*x*, *y*, *z*) as the string of integers *v* = (*x y z*), where *x*, *y* and *z* can take the code values 0, 1, 2, 3, 4. We form the function *f*(*x y z*) = *x* + *y* + *z* to measure the common code value of the data vector. To make the selection of "operate" type vectors even more accurate let us assign the weights of power-importance to the biological indices considered in the operation decision. In the gastric cancer operation decision we first concentrate our attention on the changes of *CRP*- values, which points out *CRP* as the most decisive factor. The analysis of *CRP* is followed by the judgment of age and, finally, we check the values of body weights. Hence, we state the ranking of the symptom importance as *CRP age body weight* , provided that means "more important than".

A procedure for obtaining a ratio scale of importance for a group of *m* elements (in the considered case – biological markers) was developed by Saaty (Saaty, 1978). Assume that we have *m* objects (symptoms) and we want to construct a scale, rating these objects as to their importance with respect to the decision. We ask a decision-maker to compare the objects in paired comparison. If we compare object *j* with object *k*, *j*, *k* = 1,...,*m*, then we will assign the values *bjk* and *bkj* as follows

$$1.\qquad b\_{k\circ} = \frac{1}{b\_{jk}}\ .$$

2. If objective *j* is more important than objective *k* then *bjk* gets assigned a number according to the following scheme:


If object *k* is more important than object *j*, we assign the value of *bkj*.

Having obtained the above judgments an *<sup>m</sup> <sup>m</sup>*importance matrix , 1 *m jk <sup>j</sup> <sup>k</sup> B b* is constructed. The importance weights are decided as components of this eigenvector that corresponds to the largest in magnitude eigenvalue of the matrix *B*.

Selected Algorithms of Computational Intelligence in Gastric Cancer Decision Making 541

START

Introduce *v* =(*x,y,z*)

Compute *f*(*x,y,z*)

*f*(*x,y,z*) [0.52, 3.4]?

*YES*

of gastric cancer patients. We intend to adapt the technique of an immunological algorithm based on the T cell behaviour. We use the negative selection algorithm NS proposed by

The goal of NS is to cover the non-self space with a set of detectors. For the sake of the surgery aim, already outlined in Section 2, the algorithm should lead to discrimination of the statements "operate" and "do not operate" provided that vectors characteristic of type "operate" are available. This assumption is motivated by the surgeon's intention to cure the patient from his/her cancer disease by making surgery if the patient's state allows accomplishing it. The patient data reports, which register his/her parameters in the case of operating, are clearly interpretable. However, the physician can have some doubts when he denies an operation for the patient. Therefore we have used the strings confirming the

We distinguish two steps in the surgery NS algorithm prepared on the basis of the general

1. Generation of detectors, which should possess the property vectors corresponding to the decision "do not operate" on a patient. These strings are not recognized as obviously as the strings of "operate"; that is why we get some help from the algorithm

2. Selection of the surgery settlements "operate" or "do not operate" for any patient data

In the first step a set of detectors is generated. To accomplish this task we use as an input a collection of vectors found by the method of preparing "operate" strings, which have been discussed in Section 4. Candidate detectors that match any of the "operate" type vector

GO TO NS

"operate" decision as the more convincing vectors in the entrance of NS.

NS (Dasgupta & Nino, 2008; Engelbrecht, 2007; Forrest et al., 1997):

vector due to the matching criterion concerning detectors.

Fig. 3. The flow chart of the selection of "operate" type vectors

Forrest (Forrest et al., 1997).

in generating their patterns.

*NO*

Decision "operate" vector

*YES*

Enough "operate" vectors?

*NO*
