private String getErrors(String algChoice, String matroidChoice, String oracleType) {
        error = new String[] {"", "", "", ""};
        boolean runFailed = false;
        if (algChoice.length()==0) {
            error[0] = "an algorithm,\r";
            runFailed = true;
        }
        if (matroidChoice==null) {
            runFailed = matroidIsRunFailed(error);
        }
        else if (matroidChoice.length()==0) {
            runFailed = matroidIsRunFailed(error);
        }
        if (oracleType==null) {
            runFailed = oracleIsRunFailed(error);
        }
        else if (oracleType.length()==0) {
            runFailed = oracleIsRunFailed(error);
        }
        if (runFailed) {
            return ("You must select\r" + error[0]  + error[1]  + error[2] + error[3] + "to run.");
        }
        return null;
    }